Search

Lists forthcoming papers on biochemistry, published in the June 1988 issue of the "European Journal of Biochemistry". 'Post-Translational Translocation of Polypeptides Across the Mammalian Endoplasmic Reticulum Membrane Is Dependent Upon Its Size and on the Ribosomes,' by T. Roitsch and L. Lehle; 'Characterization of the Inducible Polyamine Transporter in Bovine Lymphocytes,' by Y. Kakinuma, K.S. Montine, E.C. Henshaw and R. Panniers; 'Isolation and Characterization of a Highly Phosphorylated Troponin From Bovine Heart,' by N. Beier and K. Jacquet.

Presents a list of research papers to be published in the upcoming issues of the "European Journal of Biochemistry." "Extraction and Translation of Collagen mRNA From Fetal Calf Skin," by R. Kaufman, A. Belayew, B. Nusgens, and C. M. Lapie&rgrave;e; "Messenger RNA For Ribosomal Proteins in Xenopus laevis Oocytes," by P. Pierandrei-Amaldi and E. Beccari; "Purification and Characterization of Esterase 2B of the House Mouse, Mus musculus," by U. Lexow, A. Ronai, and O. von Deimling.

The methylation of HeLa cell ribosomal proteins has been studied by paper electrophoresis separation of the peptides produced after trypsin digestion of individual ribosomal proteins. Methylation in vivo was detected by 3H labeling of peptides from cells that had been incubated with a mixture of [methyl-3H]methionine plus [35S]methionine, the incorporation of the 3H-labeled amino acid methionine being corrected by the 35S uptake. Each methylated peptide thus represented at least one methylation site (one or more methylated amino acids and their adjacent amino acid sequence). Eleven ribosomal proteins were found to be methylated. As many as five methylation sites were present in one ribosomal protein. In several ribosomal proteins some sites were methylated when ribosome synthesis was suppressed with low levels of actinomycin D, while other sites were not. Therefore, some of the sites in a given protein were apparently methylated in mature ribosomes, while other sites were methylated during ribosome processing. The methyl-group-specific labeling of some sites, but not others, was suppressed by cycloheximide, thus suggesting that the methylation of some sites was dependent on protein synthesis. A cell-free system from cultured HeLa cells is described, which reproduces the methylation pattern of ribosomal proteins in vivo in two ways: methylation was observed both in vivo and in vitro (a) in the same ribosomal proteins; and (b) in the same methylation sites of a given ribosomal protein. In addition, our data in vitro suggest that the methylation of some human ribosomal protein sites may involve a methyl donor other than S-adenosylmethionine. [ABSTRACT FROM AUTHOR]

In this paper the question was studied whether Escherichia coli ribosomes which have undergone a specific cleavage of their 16-S rRNA by treatment with the bacteriocin cloacin DF13, are able to enter and complete an elongation cycle. As we have shown in the preceding paper in this journal, these defective ribosomes can form 70-S initiation complexes with MS2 RNA as a messenger. Binding of the second aminoacyl-tRNA (alanyl-tRNA) to the latter complexes led to the formation of fMet-Ala-tRNA which was fully puromyein-sensitive. In addition to these aminoacyl-tRNAs also the third aminoacyl-tRNA (seryl-tRNA) can be bound to defective ribosomes. Dual-label experiments showed that puromycin released all radioactivity from the ribosomes. This indicates that fMet-Ala-Ser-tRNA is formed and is translocated from the A site to the P site. Control ribosomes bind the three aminoacyl-tRNAs in a 1:1:1 ratio. The defective particles bind fMet-tRNA, Ala-tRNA and Ser-tRNA in a ratio of 1:0.5:0.25. Kinetic experiments strongly suggest that at each binding of the ternary complex aminoacyt-tRNA · EF-Tu · GTP to the A site of defective ribosomes, about half of these particles undergo irreversible inactivation. Consequently polypeptide synthesis under our conditions will come to an end after incorporation of only four or five amino acids. The particles which temporarily survive ternary complex binding are fully capable of transpeptidation and translocation. [ABSTRACT FROM AUTHOR]

Peptide studies on two acidic proteins, A1 and A2, from 50-S ribosomes of Escherichia coli indicate a closely related primary structure. 1. Amino acid compositions of the tryptic peptides of the two proteins are identical, with exception of the amino terminal peptide. 2. The N-terminal amino acid sequence of A2-protein is Ser-Ile-Thr-Lys, while that of A1-protein is N-acetyl-Ser-Ile-Thr-Lys. 3. The estimated number of 120 amino acid residues in each polypeptide chain is consistent with the physical molecular weight estimate. 4. In 50% of the polypeptide chains, in both A1- or A2-protein, a specific lysine residue is replaced by ε-N-monomethyl-lysine. [ABSTRACT FROM AUTHOR]

Translation of cellular and early vaccinia RNA in nuclease-treated lysates, derived from uninfected and vaccinia-virus-infected cells al the early stage, has been investigated. When using limiting amounts of RNA no discrimination of translation was observed in the infected cells lysates; This conclusion was confirmed by sensitive RNA competition experiments for translation in vitro and also when using two different fractionated systems for protein synthesis in vitro. This absence of detectable discrimination in vitro was established both by comparing incorporation of [35S]methionine into proteins and by analysis of the products thus synthesized by sodium dodecylsulfate gel electrophoresis. However, a modification of the translational machinery from vaccinia-virus-infected cells did occur since only the ribosomal salt wash derived from infected cells was able to reverse the inhibition of protein synthesis in vitro resulting from excess RNA (control or early). This property of vaccinia-virus-infected cell lysates may result from the synthesis of an early protein involved in translation or from a better recovery of translational factors from the infected cells., as suggested in the accompanying paper. [ABSTRACT FROM AUTHOR]

The deoxyoctanucleotide (5′-3′)d(A-A-G-G-A-G-G-T), which is complementary to the 3′ end of 16-S RNA, inhibits the formation of the complex between the 30-S subunit and MS2 RNA described in the preceding paper. If the complex is preformed, the octanucleotide cannot prevent entry of the complex into the ribosome cycle upon supplementation with the components for protein synthesis. The subunit · MS2-RNA complex is unable to bind the octanucleotide. It is concluded that in the subunit · phage-RNA initiation precursor the 16-S terminus is base-paired with a complementary MS2 RNA sequence. Edeine, aurintricarboxylic acid and antibodies against ribosomal protein S1 prevent the association of phage RNA with 30-S subunits. These compounds do not, however, inhibit the binding of (5′-3′)d(A-A-G-G-A-G-G-T) to 30-S subunits. It is concluded that the formation of the complex between MS2 RNA and 30-S subunits does not depend solely on the Shine and Dalgarno base-pairing reaction. [ABSTRACT FROM AUTHOR]

Two isogenic derivatives of Escherichia coli K12: strains EA 1 (Met-, Biot-, RCstr and EA 2 (Mei-, Biot-, RCrel) when grown in the presence of ethionine in place of methionine, synthesize ribosomes whose RNA is submethylated and whose proteins contain ethionine. Net ribosome synthesis in the presence of ethionine is greater in the RCrel strain than in the RCstr strain. The precedinig paper describes results obtained with the latter strain. Here we present further studies carried out with the isogenic RCrel strain EA 2 As in the case of the RCstr strain (previous paper) ribosomes synthesized by the RCrel strain grown in the presence of ethionine display defective association properties. A large fraction of these "ethionine" ribosomes is found as free subunits in crude extracts containing 10 mM Mg+ prepared from strain EA 2 grown in an ethionine-containing medium. These free "ethionine" subunits have sedimentation coefficients of 28 S and 45 S approximately while the "ethionine" subunits found associated as 70 S particles in crude bacterial extracts sediment at 30 S and 50 S respectively. Both classes of "ethionine" subunits (free, and associated) can be methylated in vitro in the presence of S-adenosyl methionine with or without the addition of an external source of methylases (100000 x g supernatant of a homologous crude bacterial extract) The latter observation shows that the "ethionine" subunits contain bound methylases. These enzymes do not seem to be normal ribosomal proteins nor to be bound specifically to "ethionine" ribosomes since (a) they are removed by washing the "ethionine" ribosomes with 1 M NH4Cl, and (b) they are found bound to normal methionine ribosomes from which they are also removed by washing with 1 M NH4Cl. [ABSTRACT FROM AUTHOR]

Various observations cited at the beginning of this paper and in the Discussion suggested that phalloidine, a poisonous constituent of the green mushroom Amanita phalloides, would not be toxic by itself, but would be rendered toxic previously in the liver. Using a tritiated toxic derivative of phalloidine ([³H]desmethylphalloin) we found that: (a) in rats, 60% of the administered substance are excreted unchanged in the urine within the first day. A second radioactive substance of low concentration, moving more slowly in paper chromatography turned out as a product of the self-degradation of [³desmethylphalloin; (b) respectively 98% and 99.9% of the radioactivity were extracted with methanol from homogenates of livers of rats or mice which had received [³H]desmethylphalloin 1 to 2 hours before. Aqueous homogenates of liver of poisoned rats also contained radioactivity firmly bound to a high molecular weight substance as shown by gel chromatography. The radioactive substance was totally removed from the carrier presumably ribosomal material, by adding methanol, and was identified as [³]desmethylphalloin; (e) [³H]desmethylphalloin was not metabolized on incubation with oxygen and rat liver ribosomes in a NADPH-regenerating system. A radioactive substance extracted from liver microsomes of a poisoned rat also proved to be original toxin. As a result of these experiments it can be concluded that [³H]desmethylphalloin and most probably also phalloidine are not metabolized in the livers of rats and mice. [ABSTRACT FROM AUTHOR]

Certain amino acids, like glutamine and leucine, induce an anabolic response in liver. They activate p70 ribosomal protein S6 kinase (p70S6K) and acetyl-CoA carboxylase (ACC) involved in protein and fatty acids synthesis, respectively. In contrast, the AMP-activated protein kinase (AMPK), which senses the energy state of the cell and becomes activated under metabolic stress, inactivates by phosphorylation key enzymes in biosynthetic pathways thereby conserving ATP. In this paper, we studied the effect of AMPK activation and of protein phosphatase inhibitors, on the amino-acid-induced activation of p70S6K and ACC in hepatocytes in suspension. AMPK was activated under anoxic conditions or by incubation with 5-aminoimidazole-4-carboxyamide ribonucleoside (AICAr) or oligomycin, an inhibitor of mitochondrial oxidative phosphorylation. Incubation of hepatocytes with amino acids activated p70S6K via multiple phosphorylation. It also activated ACC by a phosphatase-dependent mechanism but did not modify AMPK activation. Conversely, the amino-acid-induced activation of both ACC and p70S6K was blocked or reversed when AMPK was activated. This AMPK activation increased Ser79 phosphorylation in ACC but decreased Thr389 phosphorylation in p70S6K. Protein phosphatase inhibitors prevented p70S6K activation when added prior to the incubation with amino acids, whereas they enhanced p70S6K activation when added after the preincubation with amino acids. It is concluded that (a) AMPK blocks amino-acid-induced activation of ACC and p70S6K, directly by phosphorylating Ser79 in ACC, and indirectly by inhibiting p70S6K phosphorylation, and (b) both activation and inhibition of protein phosphatases are involved in the activation of p70S6K by amino acids. p70S6K adds to an increasing list of targets of AMPK in agreement with the inhibition of energy-consuming biosynthetic pathways. [ABSTRACT FROM AUTHOR]

UTP-modulated attenuation of transcription is involved in regulating the synthesis of pyrimidine nucleotides in Escherichia coli. Thus, expression of two genes, pyrBI and pyrE, was shown to be under this type of control. The genes encode the two subunits of aspartate transcarbamylase and orotate phosphoribosyltransferase respectively. The levels of these enzymes are inversely correlated with the intracellular concentration of UTP. Modulation of attenuation seems to be a consequence of the effect of UTP concentration on the mRNA chain growth rate. Reducing the UTP pool retards RNA polymerase movement. Mechanistically this will couple the ribosomes translating a leader peptide gene more tightly to the elongating RNA polymerase. The ribosomes will then be more prone to prevent the folding of the mRNA chains into terminating hairpin structures when RNA polymerase is at the attenuator and has to decide whether transcription should terminate or continue into the structural genes. This paper described a study of pyrBI and pyrE gene regulation in cells where the ribosomes move slowly as a result of mutation in rpsL. It appears that expression of the two genes is hyper-regulated by the UTP pool in this type of cells. Furthermore, the attenuator model can only account for the results if it is assumed that UTP-concentration dependent pausing of transcription occurs in vivo in the two pry gene leaders such that RNA polymerase waits for the coupled ribosomes before transcribing into the attenuator regions. [ABSTRACT FROM AUTHOR]

We have incorporated chloroplast ribosomal proteins (R-proteins) L12 and S18 into Escherichia coli ribosomes and examined the hybrid ribosomes for their ability to form polysomes in vivo and perform poly(U)-dependent poly(Phe) synthesis in vitro. The rye chloroplast S18 used for the experiment is a highly divergent protein (170 amino acid residues; E. coli S18, 74 residues), containing a repeating, chloroplast-specific, heptapeptide motif, and has amino acid sequence identity of only 35% to E. coli S18. When expressed in E. coli, chloroplast S18 was assembled in E. coli ribosomes. The latter formed polysomes in vivo at about the same rate as the host ribosomes, indicating that the replacement of E. coli S18 with its chloroplast homologue has only a minor, if any, effect on function. The L12 protein is much more conserved in sequence and chain length, and is known to have a very important function. The Arabidopsis chloroplast L12 used in the experiment was incorporated into E. coli 50S subunits that associated with the 30S subunits to form ribosomes, but the latter were unable to form polysomes. This result indicates functional inactivation of E. coli ribosomes by a chloroplast R-protein. To further confirm this result, we overproduced chloroplast L12 through the use of a secretion, vector and purified the protein to homogeneity. Chloroplast L12 could be efficiently incorporated in vitro into L7/12-1acking E. coli ribosomes, but the hybrid ribosomes were totally inactive in poly(U)-dependent poly(Phe) synthesis. Computer modeling of the spatial structure of all known chloroplast L12 proteins (using E. coli L12 coordinates) indicated a 'chloroplast loop' present only in chloroplast L12. The presence of this loop might have a role in the observed inactivation. Taken together with previously reported results (summarized in this paper), it would appear that the features of chloroplast R-proteins concerned with specific functions are more divergent than their assembly properties. We have previously described methods suitable for overproduction and purification of chloroplast Rproteins that are encoded in organellar DNA (≈20), but that gave poor yield for those encoded in the nuclear DNA (≈45). Here we describe a method that overcomes this problem and allows the purification of nucleus-encoded chloroplast R-proteins in milligram quantities. [ABSTRACT FROM AUTHOR]

The basic assumption in this paper is that the secondary structure era 5-S ribosomal RNA cannot be represented by a single model. We propose that the molecule can adopt, at least within the ribosome, a series of slightly different structures of nearly equal stability. The different structures arise from the existence of ambiguous base-pairing opportunities in bulged helices and the adjacent interior loops. In cubacterial 5 S RNAs there is one such an area, in eukaryotic 5-S RNAs two such areas that can give rise to structural switches. We explain how a change in secondary structure in these areas may influence the relative orientation of the surrounding helices, in other words how bulges and interior loops may serve as articulations and give rise to a flexible tertiary structure. [ABSTRACT FROM AUTHOR]

In a previous paper in this journal [Djondjurov, L., Ivanova, E. and Tsanev, R. (1979) Eur. J. Biochem. 97, 133–139], we showed that a nuclear fraction released from chromatin under a mild nuclease digestion contained an increased amount of hnRNA and the bulk of nonhistone proteins with a high metabolic rate. The present investigation has revealed that the nonhistone proteins of this fraction could be divided into three distinct metabolic groups. The first group consists of proteins with a fast turnover rate (mean half-life 30 min) which migrate into chromatin immediately after their synthesis. These proteins are predominantly acid-soluble and have relatively high molecular weights. The second group includes proteins which migrate to the nucleus more slowly and metabolize with a moderate turnover rate (mean half-life 5 h). The third group contains proteins with a more conservative metabolic behaviour. In experiments with actinomycin D it was found that the bulk of the nonhistone proteins of this fraction are not real components of the chromatin but belong to the protein moiety of heterogeneous nuclear ribonucleoprotein particles associated with chromatin. [ABSTRACT FROM AUTHOR]

The complete nucleotide sequence of the 16-S RNA from Escherichia coli has been determined using rapid RNA-sequencing gel methods. The experimental data are fully described in this paper. The specificities of the ribonucleases, especially the ribonuclease PhyI are discussed and the consequences of the persistence of stable secondary structure are considered. The proposed sequence contains 1541 nucleotides and agrees completely with the DNA sequence of the rrnB cistron deduced by Brosius, J., Palmer, M. L., Kennedy, P.J., and Noller, H. F. [Proc. Natl Acad. Sci. U.S.A. (1978) 75, 4801–4805]. But there are several cistron heterogeneities of which we described 16 single-base heterogeneities, 7 of the deletion/insertion type and 9 of the transition or transversion type. Our observations suggest the existence, among the 7 ribosome RNA cistrons, of one or two mutated ones. The respective advantages and disadvantages of both RNA and DNA sequencing methods are discussed. [ABSTRACT FROM AUTHOR]

Virginiamycin S is an inhibitor of protein synthesis in vivo. In this paper we show by equilibrium dialysis that it binds specifically to the 50-S subunit of Escherichia coli ribosomes, with one binding site per subunit. This binding is not altered by the presence of chloramphenicol, tetracycline or puromycin but is competed for by erythromycin. Using the splitting-reconstitution method, it could be demonstrated that protein L16 is absolutely required for the binding of virginiamycin S to the 50-S subunit. [ABSTRACT FROM AUTHOR]

The puromycin analogue. 5'-O-(N-bromoacetyl-p-aminophenylphosphoryl)-3'-N-L-phenylalanyl puromycin aminonucleoside, acts as an affinity label in covalently binding to 23-S RNA in the active centre of peptidyl transferase of Escherichia coli ribosomes [Greenwell, P., Harris, R. J. & Symons. R. H. (1974) Eur. J. Biochem. 49, 539-554]. The sequence of a pentanucleotide fragment of 23-S RNA to which the affinity label is attached has now been determined. In an attempt to determine the nucleotide residue to which the affinity label was attached, a 32Plabelled affinity label was reacted with ribosomal RNA, poly(A), poly(C), poly(G) and poly(U) under the conditions used for affinity labelling of ribosomes. However, no specific reaction occurred, confirming our earlier observation that this required the functional integrity of the ribosome. An alternative approach of affinity labelling ribosomes labelled by incubating E. coli in the presence of [³H]adenosine, [³H]cytidine, [³H]guanosine or [³H]uridine, showed that the affinity label was attached to a CMP residue. Effinity-labelled oligonucleotide fragments were purified for sequence analysis as follows. The free α-amino group of the affinity-label molecule attached to 23-S ribosomal [32P]RNA was coupled to biotin by reaction with the N-hydroxysuccinimide ester of biotin. After digestion of the RNA with either ribonuclease A or T1, the basic protein avidin was added to form the avidin, biotin-affinity-label-oligonucleotide fragment. Stepwise chromatography on phosphocellulose, followed (after dissociation of the avidin) by electrophoresis on DEAE-cellulose at pH 1.9 gave substantial purification of the biotin-affinity-label-oligonucleotide. From the nucleotide composition of the purified ribonuclease A and T1 fragments, the pentanucleotide sequence of G-U-C*-C-Gp was obtained, where C* represents C modified by the affinity label. [ABSTRACT FROM AUTHOR]

This paper describes three types of experiments which indicate that the binding sites for elongation factor 1 (EF-1) and elongation factor 2 (EF-2) on ascites cell ribosomes are not identical and perhaps not even overlapping. The experimental evidence presented includes direct competitive binding of labeled elongation factors to ribosomes as well as the influence of pokeweed antiviral protein and Escherichia coli anti-L7/L12 proteins on the binding and function of the two factors. It is further shown that EF-1β from Artemia salina does not function in displacing EF-1 from mouse ascites tumor cell ribosomes. These results also support our recently proposed model that EF-1 remains bound to the ribosome during the peptide chain elongation cycle. [ABSTRACT FROM AUTHOR]

When Escherichia coli 30-S ribosomal subunits are hydrolysed under mild conditions, two ribonucleoprotein fragments of unequal size are produced. Knowledge of the RNA sequences contained in these hydrolysis products was required for the experiments described in the preceding paper, and the RNA sub-fragments have therefore been examined by oligonucleotide analysis. Two well-defined small fragments of free RNA, produced concomitantly with the ribonucleoprotein fragments, were also analysed. The larger ribonucleoprotein fragment, containing predominantly proteins S4, S5, S8, S15, S16 (17) and S20, contains a complex mixture of RNA sub-fragments varying from about 100 to 800 nucleotides in length. All these fragments arose from the 5′-terminal 900 nucleotides of 16-S RNA, corresponding to the well-known 12-S fragment. No long-range interactions could be detected within this RNA region in these experiments. The RNA from the smaller ribonucleoprotein fragment (containing proteins S7, S9, S10, S14 and S19) has been described in detail previously, and consists of about 450 nucleotides near the 3′ end of the 16-S RNA, but lacking the 3′-terminal 150 nucleotides. The two small free RNA fragments (above) partly account for these missing 150 nucleotides; both fragments arose from section A of the 16-S RNA, but section J (the 3′-terminal 50 nucleotides) was not found. This result suggests that the 3′ region of 16-S RNA is not involved in stable interactions with protein. [ABSTRACT FROM AUTHOR]

When rabbit reticulocytes are incubated at 43–45°C their rate of protein synthesis rapidly decreases, compared to a control 37°C incubation. Lysates prepared fi'om cells incubated at this supra-optimal temperature have an equally decreased capacity for endogenous, but not poly(uridylic acid)-directed, protein synthesis. Subcellular fractionation traced the lesion to the crude ribosomal pellet, 0.5 M KCl ribosomal wash and postribosomal supernatant of the temperature-shocked cells. Preparation of purified ribosomal subparticles showed, however, that they were as active as the control in protein synthesis. In this paper we present evidence that the decreased activity of the heated lysate, 0.5 mM KCl wash and postribosomal supernatant is due to an inhibitor and can be overcome by the addition of 0.5 M KCl or supernatant from control cells. The results are discussed in terms of the inactivation of a component, essential for initiation of endogenous protein synthesis, which is probably partitioned between ribosomes and supernatant. We also suggest that the decreased protein synthetic activity of the heated cells may be related to their decreased synthesis of haem. [ABSTRACT FROM AUTHOR]

The confronmation in solution of duck and rabbit globin mRNA, and of the duck mRNA in the mRNA · protein particle, has been investigated by optical methods and also by the use of the dye ethidium bromide which becomes highly flourescent when intercalated into the double-stranded regions of a nucleic acid. On the basis of the properties of this dye and on the ability of homopolyribonucleotides to form double-stranded structures we have, in addition, developed a simple and sensitive assay for the detection and quantitisation of sequences rich in a particular residue that may be present in an RNA chain. In solutio, 45 to 60% of the nucleotides of duck globin mRNA were found to be in bihelical regions. A similar degree of secondary structure was found in rabbit globin mRNA (this paper), as well as in calf lens mRNA and mRNAs from ewe mammary gland (other results). All samples of globin mRNA examined in this work contained a sequence of poly(A), which has poly(U) binding properties similar to that of synthetic poly(A): no specific interaction between the poly(A) sequence and the rest of the molecules can be detected. The fraction of adenosine residues within these poly(A) segments represents 4% in rabbit mRNA and 8 to 9% in duck mRNA. An additional adenosine-rich segment interspersed with guanosine and possibly residues, was also detected in one duck mRNA sample. The RNA in the duck mRNA · protein particle is also highly structured. The melting profile in the range of 20 to 65° C is quite similar to that of free mRNA and the ability of ethidium bromide to intercalate is reduced to the extent of 70%. Yet the dichroïc spectra of free and bound mRNA are significantly distinct. These data suggest that free and protein-bound mRNA may have a very similar degree of secondary structure but with distinct detailed conformation in bihelical regions (change in base tilting for example). Direct evidence has been obtained that proteins stick to the poly(A) segment in the particle since the fraction of adenosine residues detectable by our poly(A) titration procedure is reduced to 50% of that observed in the free mRNA. [ABSTRACT FROM AUTHOR]

The effects of ricin on the different steps of the elongation cycle of protein synthesis in a rabbit reticulocyte cell-free system are studied in this paper. The toxin most probably acts by catalytically inactivating the ribosomes, since a single molecule of the toxin can inactivate 300 ribosomes for poly(U)-directed phenylalanine incorporation. The effect of the toxin on the ribosome is irreversible. Ricin specifically inhibits elongation-factor-l-dependent aminoacyl-tRNA binding to ribosomes but has no effect on the non-enzymic binding of aminoacyl-tRNA. Ricin also inhibits formation of the complex elongation-factor-2 · ribosome · nucleotide with GTP, GDP or GMP-P(CH2)P. However, the toxin has no effect on translocation. These apparently conflicting results arc discussed in this study. [ABSTRACT FROM AUTHOR]

A technique which releases ribosomes from membranes without the use of detergent described in the preceding paper is shown to allow the separation of two distinct pools of poly(A)-containing RNA in microsomes. Thus, using preparations from mouse myeloma tissue-culture cells, essentially 100 % release of immunoglobulin mRNA occurs under conditions in which only 50-60 % of the total microsomal poly(A)-containing RNA is released. The RNA which is not released is principally mitochondrial ribosomal RNA and the method thus provides a good preparative procedure for this fraction. Messenger ribonucleoprotein particles involved in immunoglobulin biosynthesis have been prepared from the released material. The heavy-chain mRNA-containing particle sediments in a neutral sucrose gradient at about 22 S, and that containing the light-chain mRNA at about 18 S. The ribosome-release technique has been used for the rapid preparation of light-chain mRNA in good yield and at over 60 % purity after a single sucrose gradient centrifugation. Further purification has been achieved by polyacrylamide gel electrophoresis. Using [32P]RNA, the contaminants can be estimated directly at the chemical leveI using a fingerprint assay. [ABSTRACT FROM AUTHOR]

In this paper we demonstrate that two compounds which are known to enhance the permeability of membranes to potassium, valinomycin, a cyclic dodecapeptide and dicyclohexyl-18-crown-6, a macrocyclic polyether, inhibit protein synthesis in reticulocytes and that this inhibition is not primarily due to changes in the intracellular potassium concentration. No effect is obtained by adding the drugs to a cell free system and the inhibition observed is likely to be membrane mediated. Dicyclohexyl-18-crown-6 and low concentration of valinomycin (10 nM) act reversibly probably by interacting with the lipid phase of the membrane. This interaction in turn affects the protein synthesizing apparatus by affecting ribosomal functions. Ribosomes once isolated from treated cells are perfectly normal in structural and functional respects. High concentrations of valinomycin, which change the K+ gradient between the inside and the outside of the cell, affect the protein synthesizing apparatus of reticulocytes irreversibly by blocking incorporation of amino acids at the level of elongation or termination. Ribosomes isolated from cells treated with high valinomycin concentrations are mostly in the form of polysomes which are inactive in cell free protein synthesis. The high valinomycin block on the ribosomal fraction can be relieved either by washing ribosomes with high salt or with puromycin. It is believed that with high concentrations of valinomycin an inhibitor is released (probably from the membrane) and attached to the ribosomes. This high valinomycin effect is believed to by a supplementary phenomenon which when added to the effect of low valinomycin renders the inactivation of ribosomal functions irreversible.

The two types of 30-S · 50-S couples described in the preceding paper, differ markedly in their sensitivity to hydrostatic pressure evoked during centrifugation in sucrose gradients. The sedimentation coefficient of about 60 S recorded with couples formed from native subunits is only apparent, the real a value being 70 S. The latter couples can be stabilized against pressure-induced dissociation by bound tRNA. On the other hand this binding renders couples formed from derived subunits more sensitive to this dissociation. As the factor determining this intriguing difference in pressure sensitivity lies in the 50-S subunit, a comparative analysis of a number of ribosomal constituents has been performed for native and derived 50-S particles. No qualitative differences in the proteins L1–L34 have been detected. Quantitative differences cannot yet be excluded. It is considered unlikely that differences in rRNAs or low-molecular-weight components arc responsible for the distinct association behaviour. Partial reconstitution of ribosomal γ-cores and split proteins detached by CsCl reveals that the determinant factor is located in the core particles. This suggests that native and derived 50-S subunits do not differ in conformation only. The possibility may be envisaged therefore, that the two types of 50-S differ in a ribosomal protein. [ABSTRACT FROM AUTHOR]

As found previously, 70 to 75% of the RNA present in previtellogenic oocytes of Xenopus laevis (average diameter: 50 to 150 μm) is 5-S RNA and transfer RNA. In this paper, we show that most of the RNA of the small oocytes is stored in nucleoprotein particles sedimenting at 58 S and 42 S. These particles are no longer detectable in vitellogenic oocytes (average diameter: 375 to 1100 μm) which accumulate ribosomes very rapidly. The 58-S particles contain mainly high-molecular-weight RNA. This RNA has a base composition close to that of DNA. Its main component sediments at about 19 S. The 42-S particles contain more than half of the RNA and a quarter of the protein present in homogenates of small oocytes. The only RNA species found in the 42-S particles are 5-S RNA and tRNA. The molar ratio of tRNA to 5-S RNA in the 42-S particles is 3:1. 5-S RNA is distributed as follows in the small oocytes: less than 1% of the total cell content is bound to the ribosomes; about 50% is in the 42-S particles and the remainder is apparently free in the cell sap. By its base composition and its hybridization properties 5-S RNA from the 42-S particles cannot be distinguished from 5-S RNA of the cell sap and from 5-S RNA of somatic cells. About 900 of the total tRNA content of the oocyte is included in the 42-S particles. The remaining 10% is either free or bound to the ribosomes. No difference was noticed in the hybridization properties of tRNA which is inside the 42-S particles and tRNA which is outside these particles. The 42-S particles present in homogenates of previtellogenic oocytes are not artifacts. These particles are probably storage particles in which 5-S RNA and tRNA produced in excess during the initial period of oogenesis are kept for many months until the ribosomes begin to accumulate. The role of the 58-S particles remains unknown. [ABSTRACT FROM AUTHOR]

The binding of purified Gly3-Phe-tRNA to Escherichia coli ribosomes was compared to that of crude Gly3-Phe-tRNA (containing bulk tRNA). Gly3-phe-tRNA from the purified preparation binds preferentially to the P site (peptidyl site) at both a high (30 mM) and a low (10 mM) magnesium acetate concentration, while peptidyl-tRNA from the crude preparation bound more to A site (aminoacyl site) than to the P site at 30 mM magnesium acetate under the same experimental conditions. The addition of tRNAPhe to the purified Gly3-Phe-tRNA preparation strongly inhibited the binding at 10 mM. At 30 mM Mg2+ the addition of the same amount of tRNAPhe caused the Gly3-Phe-tRNA to bind partially to the A site, but did not inhibit the total amount of Gly3-Phe-tRNA which binds to the ribosomes. The binding of purified Phe-tRNA in the presence of T factor and GTP is not inhibited by tetracycline. However, tetracycline strongly inhibited the enzymatic binding of Phe-tRNA when tRNAPhe was added. From the results presented in this paper it is proposed that in the presence of poly(U), Phe-tRNA or peptidyl-tRNAPhe can bind to A sites only of those ribosomes which have their P site occupied by tRNA or one of its derivatives (aminoacyl-tRNA or peptidyl-tRNA). [ABSTRACT FROM AUTHOR]

In this paper an efficient procedure is described for the isolation of polysomes from tissue culture cells. optimal yields, especially of the heavier classes of polysomes can only be obtained at a rather high KCl concentration in the presence of nonionic detergent. Evidence is provided that the lower polysomal yield after extraction at low salt concentration is not due to breakdown of the polysomes by RNAase. Furthermore, the yield of polysomes is pH dependent only at low salt concentration, while at high salt concentration no influence of the pH is observed. Refreshing of growth medium several hours before harvesting the cells, increases the ratio of polysomes to 80 S monomers. [ABSTRACT FROM AUTHOR]

It is well know that protein synthesis stopped either by chloromycetin or by starvation of an essential amino acid for a RC relstrain, ribosomal RNA synthesis continues, but products do not appear in 50 S and 30 ribosomes. It has also been shown that 5 S RNA synthesis is altered by the addition of chloromycetin but in an unknown manner. In this paper we report that: (a) during amino-acid starvation of a starvation of RCrel strain of Escherichia coli, 5 S RNA is transcribed as 5 S relax RNA located outside the ribosomes, in the supernatant fraction; (b) this 5 S RNA which is slightly longer than the normal product is convertible into a true 5 S RNA when protein synthesis is restored after blockage of RNA synthesis by actinomycin ;(c) part of the 23 S RNA from a 25 S particle appears after resumption of protein synthesis in a 40 S parcel which contains normal 5S RNA; (d) a pool of 5 S precursor RNA exists outside the 50 S ribosome. This 5 S precursor RNA is isolated; (e) this precursor which is isolated from the 105000xg supernatant fraction after pulse labeling, migrates on gel electrophoresis between 5 S relax RNA and true 5 S RNA. [ABSTRACT FROM AUTHOR]

1. The distribution of ribosomal particles between the soluble and membrane fractions of exponential-phase cells of Bacillus licheniformis was studied. The cells were very gently lysed by a combined treatment with lysozyme and Brij 58 in 10 mM. Tris-buffer, pH 7.6, with 60 mM K+, 10 mM Mg2+, 0.5 mM spermine and 0.75 mM spermidine. The proportion of the ribosomal material present in the membrane fraction was estimated after solubilization of the membranes by the combined action of Brij 58, deoxyribonuclease and lipase. 2. Under these conditions of lysis 96% of the total ribosomal material, consisting of subunits (12%) monosomes (20%) and polyribosomes (68%) and most of the cellular DNA, is found to be membrane-bound. 3. In the soluble fraction, containing only 4% of the total cellular amount of the ribosomal material, only subunits and 70S particles and no polyribosomes are found. 4. DNA does not seem to be involved in the binding of the ribosomal material to the membranes. 5. The results will be discussed considering the question of whether the distribution described in this paper represents the true distribution in vivo of ribosomes. [ABSTRACT FROM AUTHOR]

N-terminal acetylation of the lens protein α-crystallin has been studied in a lens cell-free system. This system is capable of synthesizing de novo α-crystallin, a protein with acetylmethionine as N-terminus. When [35S]Met-tRNAfMet is used as radioactive precursor only the α-crystallin chains are labeled in the N-terminal position. This phenomenon enables the study of the process of acetylation. Newly synthesized polypeptides could be separated according to chain length. Electrophoretic analysis of thermolytic peptides revealed that acetylation of the N-terminus occurs while the chain is still on the ribosome. It is concluded that the N-terminal acetylation takes place after chain initiation and before completion of the polypeptide chain. [ABSTRACT FROM AUTHOR]

Six ribosomal proteins are specific to higher plant chloroplast ribosomes [Subramanian, A.R. (1993) Trends Biochem. Sci. 18 , 177–180]. Three of them have been fully characterized [Yamaguchi, K., von Knoblauch, K. & Subramanian, A. R. (2000) J. Biol. Chem. 275 , 28455–28465; Yamaguchi, K. & Subramanian, A. R. (2000) J. Biol. Chem. 275 , 28466–28482]. The remaining three plastid-specific ribosomal proteins (PSRPs), all on the small subunit, have now been characterized (2D PAGE, HPLC, N -terminal/internal peptide sequencing, electrospray ionization MS, cloning/ sequencing of precursor cDNAs). PSRP-3 exists in two forms (α/β, N-terminus free and blocked by post-translational modification), whereas PSRP-2 and PSRP-4 appear, from MS data, to be unmodified. PSRP-2 contains two RNA-binding domains which occur in mRNA processing/stabilizing proteins (e.g. U1A snRNP, poly(A)-binding proteins), suggesting a possible role for it in the recruiting of stored chloroplast mRNAs for active protein synthesis. PSRP-3 is the higher plant orthologue of a hypothetical protein (ycf65 gene product), first reported in the chloroplast genome of a red alga. The ycf65 gene is absent from the chloroplast genomes of higher plants. Therefore, we suggest that Psrp-3/ycf65 , encoding an evolutionarily conserved chloroplast ribosomal protein, represents an example of organelle-to-nucleus gene transfer in chloroplast evolution. PSRP-4 shows strong homology with Thx, a small basic ribosomal protein of Thermus thermophilus 30S subunit (with a specific structural role in the subunit crystallographic structure), but its orthologues are absent from Escherichia coli and the photosynthetic bacterium Synechocystis . We would therefore suggest that PSRP-4 is an example of gene capture (via horizontal gene transfer) during chloro-ribosome emergence. Orthologues of all six PSRPs are identifiable in the complete genome sequence of Arabidopsis thaliana and in the higher plant... [ABSTRACT FROM AUTHOR]

The procedures developed earlier (Friedrich and Woolley, preceding paper in this journal) for probing electrostatic potential with the fluorescein label were applied to transfer RNA. By using tRNA species that contain chemically reactive bases we were able to label these bases with fluorescein derivatives and thus to 'map' the electrostatic potential around the molecule. Both the electrostatic potential and the fluorescence emission anisotropy data that were obtained at the same time could be understood in terms of the well-known, paradigmatic crystal structure of tRNAPhe. However, within the distribution of the various tRNA species, tRNAfMet appeared to occupy an extreme position, which suggests a relation between the conformation in solution and the initiation function of this molecule. Comparison with theoretical predictions by others of the electrostatic potential map of tRNA showed agreement in respect of trends, but the values of the potentials measured were orders of magnitude lower than predicted. This we attribute primarily to solvation. [ABSTRACT FROM AUTHOR]

Ribosomes have been shown to contain a proteolytic activity, characterized as an endopeptidase with serine in the active center. The enzyme has been given the name cathepsin R, following the recommendations of Barrett et al. tin a publication from the Cold Spring Harbor Laboratory, New York) for naming new proteinases. The present paper contains evidence that cathepsin R in rat liver ribosomes is present in a cryptic form. Upon dissociation of ribosomes to subunits (and to minor extent also by 0.5 M KCI washes), the cryptic proteinase is released. Activation of the released cathepsin R is effected by equilibration with 2 M NaCI/0.05 M sodium acetate, pH 4.8. The molecular weight of free cathepsin R is 25000–30000. [ABSTRACT FROM AUTHOR]

A resistance gene, carB, originally isolated from the carbomycin-producing organism. Streptomyces thermotolerans, confers on Streptomyces lividans high-level resistance to the drug. However, ribosomes from S. lividans expressing carB show only moderate resistance to this macrolide in vitro, although they are highly resistant to the action of lincosamide antibiotics. The carB product monomethylates the amino group of the adenosine residue located at position 2058 in 23S ribosomal RNA. In contrast, ribosomes from S. lividans expressing ermE, in which 23S RNA is dimethylated at this same position, are much more highly resistant to macrolides and insensitive to lincosamides. [ABSTRACT FROM AUTHOR]

The GTPase activity of purified EF-1α from calf brain has been studied under various experimental conditions and compared with that of EF-Tu. EF-1α displays a much higher GTPase turnover than EF-Tu in the absence of aminoacyl-tRNA (aa-tRNA) and ribosomes (intrinsic GTPase activity); this is due to the higher exchange rate between bound GDP and free GTP. Also the intrinsic GTPase of EF-1α is enhanced by increasing the concentration of monovalent cations, K+ being more effective than NH4+. Differently from EF-Tu, aa-tRNA is much more active than ribosomes in stimulating the EF-1α GTPase activity. However, ribosomes strongly reinforce the aa-tRNA effect. In the absence of aa-tRNA the rate-limiting step of the GTPase turnover appears to be the hydrolysis of GTP, whereas in its presence the GDP/GTP exchange reaction becomes rate-limiting, since addition of EF-1β enhances turnover GTPase activity. Kirromycin moderately inhibits the intrinsic GTPase of EF-1α; this effect turns into stimulation when aa-tRNA is present. Addition of ribosomes abolishes any kirromycin effect. The inability of kirromycin to affect the EF-1α/guanine-nucleotide interaction in the presence of ribosomes shows that, differently from EF-Tu, the EF-1α · GDP/GTP exchange reaction takes place on the ribosome. [ABSTRACT FROM AUTHOR]

The complete amino acid sequence of ribosomal protein L2 from the moderate thermophile Bacillus stearothermophilus has been determined. This has been achieved by the sequence analysis of peptides derived by enzymatic digestion with Staphylococcus aureus protease, trypsin and chymotrypsin, as well as by chemical cleavage with o-iodosobenzoic acid. The protein contains 275 amino acid residues and has a calculated molecular mass of 30201 Da. Comparison of this sequence with sequences of the corresponding proteins from Escherichia coli and from spinach and tobacco chloroplasts reveals that 60% of the residues of protein L2 from B. stearothermophilus are identical to those of the protein from E. coli and 45% are identical to those found in the two chloroplast proteins. There are extended regions of totally conserved sequence at positions 54-58 (GGGHK), 81-86 (EYDPNR), and 224-230 (MNPVDHP) in all four proteins. [ABSTRACT FROM AUTHOR]

The regulation of ribosomal proteins (r-proteins) and their mRNAs (rp-mRNAs) was studied in the L6 myoblast, a mammalian cell line which can undergo myogenesis. Upon terminal differentiation, the rate of accumulation of mature ribosomes dropped to approximately 25% of the rate found in undifferentiated myoblasts. Despite the drop in the rate of ribosome accumulation and the rate of rRNA synthesis following terminal differentiation, the rate of r-protein synthesis remained constant. The excess r-protein synthesized in myotubes was quickly degraded. The levels of rp-mRNAs were assessed before and after differentiation. Over 90% of the rp-mRNAs were found on polysomes in both myoblasts and myotubes and represented similar fractions of total poly(A)-rich mRNA. The half-lives of the rp-mRNAs averaged approximately 11 h in both myoblasts and myotubes. In vitro nuclear transcription measurements of a representative rp-mRNA (L32 mRNA) revealed that following differentiation, its rate of synthesis relative to the overall transcription rate dropped by approximately 26% in myotubes while the rate of transcription of rRNA dropped by approximately 77%. These results indicate that the coordination of r-protein and rRNA synthesis observed in myoblasts was uncoupled in myotubes at the level of transcription. [ABSTRACT FROM AUTHOR]

The addition of nutrients to long-time-starved-cells of Tetrahymena pyriformis leads to a 50-60-fold increase in the rate of synthesis of ribosomal proteins (r-proteins). This is achieved by a 6-fold increase in the relative rate of r-protein synthesis and a 8-10-fold increase in the rate of total protein synthesis. Synthesis of r-proteins constitutes one third of total cellular protein synthesis 2-4 h after refeeding and the absolute rate of r-protein synthesis is approximately three-times greater than in exponentially growing cells. The synthesis of the individual r-proteins is coordinately regulated during a nutritional shift-up, and de novo synthesized r-proteins are stable. Addition of actinomycin D prevents the increase in the rate of r-protein synthesis. The rates of synthesis of rRNA and r-protein increase in concert, implying coordinate regulation. Furthermore, a comparison of the observed accumulation of r-proteins with the predicted accumulation based on the accumulation of rRNA suggests that rRNA and r-protein are synthesized in a stoichiometrically balanced way during the entire refeeding period. [ABSTRACT FROM AUTHOR]

A high-molecular-mass nucleolar protein (100-kDa protein) is associated with nascent pre-rRNA and preribosomes in Chinese hamster ovary cells. We have prepared antiserum against the 100-kDa protein and we have used it to study the intracellular localization and the possible processing of this protein. Serologically related proteins were detected in the nucleolus and in ribosomes. Proteins of various subcellular fractions were separated by sodium dodecyl sulfate/polyacrylamide gel electrophoresis, transferred to nitro- cellulose filters, reacted with serum and the protein-immunoglobulin complexes were revealed by 125I-labeled protein A In the nucleolus, four proteins with molecular masses of 100 kDa, 95 kDa, 76 kDa and 70 kDa were thus visualized. In the ribosomes, two proteins (of 100 kDa and 76 kDa) gave a strong reaction while six others (of 70 kDa, 60 kDa, 50 kDa, 30 kDa, 21 kDa, 18 kDa) reacted slightly. By immunological precipitation of total cell extracts, we have shown that the 100-kDa protein antiserum cross-reacts with live proteins with molecular masses of 120 kDa, 100 kDa, 95 kDa, 70 kDa and 60 kDa. Specific degradation of the 100-kDa protein into similar peptides with molecular masses of 95 kDa, 76 kDa, 70 kDa, 60 kDa and 50 kDa can be achieved by incubation of isolated nucleoli or of purified 100-kDa protein in vitro. Cleavage of the protein is due to a thiol endoprotease which is tightly bound to the 100-kDa protein. Possible relations between the maturation of this preribosomal protein into ribosomal proteins and the processing of preribosomal RNA into mature ribosomal RNA are discussed. [ABSTRACT FROM AUTHOR]

The nucleotide sequence of wheat (Triticum aestivum) 5.8-S ribosomal RNA has been re-examined using partial chemical degradation with high-temperature sequencing gels and oligonucleotide analysis. The results clarify previously ambiguous residues and add two additional nucleotides, G127 and G135 to the sequence. Estimates of the secondary structure suggest that 5.8-S rRNAs of higher plants differ from previous examples in having more open G + C-rich and A + U-rich stems. S1 ribonuclease digestion was used to probe this secondary structure; the data generally support the 'burp gun' model proposed for all 5.8-S rRNAs but are also consistent with a more open A + U-rich stem. Diethyl pyrocarbonate reactivity was used to probe the topography of this RNA in wheat ribosomes. The results indicate that the G + C-rich and A + U-rich stems are accessible to chemical modification in the wheat ribosome and suggest that the A + U-rich stem undergoes a significant conformational change when the molecule associates into ribosomes. [ABSTRACT FROM AUTHOR]

Focuses on the mutant elongation factor Tu which does not immobilize the ribosome upon binding of kirromycin. Search for the primary site of inhibition in the elongation cycle; Formation by the elongation factor TuB[sub o] of a complex with aminoacyl-tRNA and guanosine triphosphate; Ability of the complex to bind to ribosomes programmed with poly; Recessive nature of the tuf B mutation in cells producing kirromycin-resistant elongation factor TuA and TuB[sub o]; Polypeptide synthesis; Ability to bind the antibiotic.

A ribonucleoprotein prepared by strong ribonuclease digestion of a complex of 16-S ribosomal RNA and proteins S4 and S20 from Escherichia coli has been characterized; its nucleotide sequence, the positions of enzyme cuts and the sequence excisions have been placed in the completed sequence of 16-S RNA. The positions and yields of enzyme cuts, and excisions of sequence, are compared with those of various ribonucleoproteins prepared with S4 or S20 alone, and with the ribonuclease-resistant S4 RNA prepared from renatured 16-S RNA in the absence of ribosomal protein. These data yield important information on the topography and organization of the 5′ third of the 16-S RNA which is selectively maintained in its native conformation by the bound proteins; they also provide criteria for testing secondary structural models of this region of 16-S RNA. [ABSTRACT FROM AUTHOR]

Sindbis virus 42-S and 26-S RNAs labeled with 32P were purified from infected chick embryo fibroblasts. The RNAs were incubated in the presence of a wheat germ cell-free translating system under conditions that yielded 40-S and 80-S initiation complexes. After digestion with RNase A, ribosome-protected fragments were isolated by polyacrylamide gel electrophoresis and compared with respect to number, size, cap content and oligonucleotide composition. The two RNA species yielded several fragments of chain length about 35-40 nucleotides from 80-S complexes and up to 60-65 nucleotides from 40-S complexes. The 5'-terminal capped sequence, m7GpppA-U-G that is present in both Sindbis virus RNAs, was not retained in any of the ribosome-protected fragments. Fingerprint analyses indicated that the fragments derived from 40-S and 80-S initiation complexes of each species of RNA were overlapping, but the fragments from 42-S and 26-S RNAs were unrelated. The complexity of the fingerprints were consistent with protection of a single, different initiation site in each Sindbis virus RNA. [ABSTRACT FROM AUTHOR]

The effect of bacteriocin (cloacin DF13) treatment of Escherichia coli ribosomes on initiation of protein synthesis has been studied in detail. In agreement with out previous findings [Baan et al. (1976) Proc. Natl Acad. Sci. U.S.A, 73, 702–706] it is shown that 70-S initiation complexes can be formed with cloacin-treated ribosomes, but that the initiation factor IF-1 does not function properly. The following pleiotropic effects of this factor have been studied: (a) the acceleration of ribosomal subunit exchange with 70-S couples; (b) the stimulation of the IF-3-mediated dissociation of 70-S ribosomes; (c) the stimulation of 30-S initiation complex formation; (d) the enhancement of the rate of release of IF-2 from 70-S initiation complexes. The effects (a) and (b) are virtually abolished after cleavage of 16-S rRNA. The effect (d) is only partially reduced whereas effect (c) seems to be unimpaired. It is concluded that 70-S initiation complex formation with cloacin-treated ribosomes suffers from improper functioning of IF-1 in the generation of active subunits from 70-S tight couples. This is the only effect on initiation. It can he compensated for by adding more IF-3. The data provide functional evidence that 16-S rRNA is involved in ribosomal subnnit interaction. [ABSTRACT FROM AUTHOR]

After digestion of protein S4 with trypsin, all 32 tryptic peptides were isolated. Their amino acid compositions were analyzed and the sequence of the amino acids within the tryptic peptides was determined by means of a solid-phase peptide sequenator and by exopeptidases. Alignment of the tryptic peptides was established by analyzing and partially sequencing peptides isolated after digestion of the $4 protein with chymotrypsin, thermolysin and a glutamic-acid-specific protease. Further information about the alignment of peptides came from treatment of S4 with CNBr and with a lysine-modifying reagent. Protein S4 consists of 203 amino acids (Asp8, Asn8, Thr6, Ser10, Glu16, Gln10, Pros, Gly15, Ala18, Va116, Cys1, Met3, Ile8, Leu20, Tyr8, Phe4, His3, Lys20, Arg22 and Trp1) and has a molecular weight of 22550. The basic amino acids are clustered in five regions. Many short repetitions mainly with charged amino acids occur. A prediction is made for regions with or α-helices and with β-sheets. [ABSTRACT FROM AUTHOR]

The study of polysomal formation in the ts-136 thermo-sensitive yeast mutant indicates that ribosomes are assembled with an mRNA, which is in a structure tightly bound to membranes, and are then released into the soluble cytoplasmic fraction. This has been observed by studying the recruitment of ribosomes when glucose is added to glucose-starved cells and when transport of mRNA is permitted by shifting the mutant to the permissive temperature. A soluble cytoplasm and a fraction becoming soluble after sodium deoxycholate treatment of a rapidly sedimenting structure have been characterized. The former contains the majority of polysomes, free 80-S monomers and almost all of the ribosomal subunits. The latter fraction is composed of bound 80-S monomers and polysomes, but lacks ribosomal subunits. Treatment of the rapidly sedimenting structure with pancreatic ribonuclease produces the release of 80-S monomers, with EDTA the release of an equal proportion of both ribosomal subunits, and with sodium deoxycholate the release of 80-S monomers and polysomes. These findings are consistent with the assumption that bound ribosomes are assembled with an mRNA which is tightly bound to this rapidly sedimenting structure, presumably membranes. From the operational viewpoint this fraction is called the "membrane." During the process of polysomal formation ribosomes are recruited more rapidly in the "membranes" than in the soluble cytoplasm. Since "membranes" do not accumulate polysomes and contain only a small fraction of the total amount of ribosomes, the result is consistent with the assumption that either there is a higher turnover of bound versus free polysomes or bound polysomes are the precursors of free polysomes. The latter assumption is more likely since we have shown previously (a) that in yeast, transport is coupled with the translation of bound mRNA, (b)that this mRNA is tightly bound to a structure which sediments very rapidly and becomes soluble only after sodium deoxycholate treatment, and (c) when cycloheximide is added during the recruitment of ribosomes there is accumulation of membrane-bound ribosomes. [ABSTRACT FROM AUTHOR]

Smooth and rough endoplasmic reticulum and free ribosomes from rat liver each show cyclicAMP-stimulated protein kinase activity utilizing exogenous substrates. The protein kinases of smooth and rough endoplasmic reticulum can be divided into two classes, one which is extracted by ionic media, and one more firmly attached enzyme fraction which is solubilized by Triton X-100. The protein kinase of free ribosomes is extracted by ionic media. All the three microsomal fractions support an endogenous phosphorylation of proteins which is only slightly stimulated by cyclic AMP. The endogenous phosphorylation shows two pH optima at pH 6.5 and 8.5. The phosphate is incorporated into seryl and threonyl residues of several protein species. Two major phosphoproteins are present in both smooth and rough endoplasmic reticulum, while a third major phosphoprotein is present only in the smooth fraction. There are also several minor phosphoproteins in the two fractions. The endogenous phosphorylation is initially rapid, especially in smooth and rough endoplasmic reticulum where it reaches a maximum after 10—15 rain incubation. The endogenously phosphorylated microsomal fractions also support an endogenous dephosphorylation, which is rapid initially, but which leaves approximately 60% of the phosphoryl groups unhydrolyzed. Like the protein kinase the proteins of smooth and rough endoplasmic reticulum which can undergo endogenous phosphorylation can be divided into two classes, one which is extracted in ionic media and one more tightly bound which is solubilized by Triton X-100. Protein kinase, cyclic-AMP-binding material and protein substrates extracted from smooth and ruogh endoplasmic reticulum by salt or detergent all show recoveries substantially exceeding 100%, suggesting that these activities are partly masked while associated with membrane material. [ABSTRACT FROM AUTHOR]

Both rRNA and protein components of Escherichia coli ribosomes have been specifically labelled without any important loss of activity for polyphenylalanine synthesis in the cell-free system. Three adenylic residues per 70-S ribosome were labelled by an anthracenyl derivative and the ribosomal proteins by dansylation of four amino acid residues per 70-S particle. The association between the two complementary subparticles, the formation of the binary and ternary complexes in the presence of mRNA and tRNA were investigated using the concomitant measuring of fluoroscence intensity and polarisation of the two kinds of labels. The formation of these complexes involves the rRNA and the ribosomal protein components of the 30-S and 50-S subparticles directly and/or indirectly. The mobility of the messenger bound to the 70-S ribosome in the presence of tRNA is indicated by use of a polyadenylic acid labelled with the same marker ss that for rRNA. Reversible conformational changes are observed during acidic-alkaline titrations and melting curves of fluorescent ribosomal particles. The irreversible denaturation occurs at the same pH and melting temperature for the rRNA and the ribosomal components: The results are interpreted in terms of highly specific interactions between the rRNA and the proteins, slight modification in the strength and/or nature of these interactions leading to a conformational change of the whole ribosomal particle. [ABSTRACT FROM AUTHOR]

The existence of three stable forms of the 5.8-S ribosomal RNA species in Saccharomyces cerevisiae has been demonstrated. The major form constitutes approximately 90% of the total 5.8-S RNA and the two minor forms each constitute approximately 5%. The nucleotide sequence of the major form begins pA-A-A-Cp. The sequences of the minor forms begin pU-A-U-U-A-A-A-A-A-Cp and pA-U-A-U-U-A-A-A-A-A-Cp. The remainders of the sequence of all three forms appear to be identical. [ABSTRACT FROM AUTHOR]