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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]

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]

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]

16-S RNA and five pure ribosomal proteins (S3, S4, S6, S7 and S8) from Escherichia coli 30-S subunits were studied by circular dichroism in regard to the reconstitution of biologically active subunits. A small structural variation upon heating could be measured for RNA. It cannot be interpreted in terms of stacking or disruption of hydrogen bonds. However, most proteins underwent important structural modifications when heated to 42 °C in reconstitution solvent. This effect was not dependent on the presence of magnesium salt. The relative amounts of secondary structure of native and heat-denatured ribosomal proteins were calculated by using three reference curves obtained from standard proteins, the exact secondary structure of which has been determined by X-ray crystallography. In contrast with earlier results, about 18 %, β-structure was detected in native proteins. This discrepancy can most probably be attributed to the calculation method used. Results are discussed in relation to reconstitution of ribosomes. [ABSTRACT FROM AUTHOR]

Protein A is a cell wall constituent of Staphylococcus aureus. After being synthesized on the ribosomes, the protein A molecules are linked to the peptidoglycan. This is a very rapid reaction which is completed within approximately 1 min; it is suggested that the molecules leave the ribosomes and are then directly incorporated into the peptidoglycan without passing a soluble cytoplasmic stage. The synthesis of protein A de novo and peptidoglycan take place independently of each other. Also, the incorporation of protein A into the cell wall proceeds when the synthesis of peptidoglycan has been completely inhibited by vancomycin, i.e. the synthesis of peptidoglycan is not essential for the incorporation of protein A. It is therefore concluded that protein A can be linked to pre-existing peptidoglycan chains. [ABSTRACT FROM AUTHOR]

The nature of the interaction of membrane-bound polysomes with the endoplasmic reticulum has been studied in MOPC 21 mouse plasmocytoma tissue-culture cells which secrete an immunoglobulin G. Treatment of microsomes at high salt concentrations (500 mM KCl) results in the detachment of 40-45 % of the bound ribosomes. This released ("loose") fraction is predominantly monosomal in contrast to the remaining "tight" polysomes. It is shown that both ribosomal fractions contain immunoglobulin light-chain mRNA which argues against a functional distinction between them in the cell. Polysomes have been dissociated to apparently undegraded ribosomal subunits at 0 °C by incubation with puromycin in the presence of a magnesium ion buffer. Application of this procedure to membrane-bound polysomes results in partial release of ribosomal subunits from the membrane. The ribosomal material which is not so released sediments predominantly at 60 S and this fraction can be detached by subsequent washing at 500 mM KCl. Thus, by use of the polysome-dissociating procedure together with high salt concentrations, essentially total release of the ribosomal components can be obtained. The results indicate that the salt-labile interactions are mediated via the large ribosomal subunits and are the only anchoring forces to the membrane at early stages of protein synthesis. The tight membrane-bound polysomes result from the additional anchoring effect of the polypeptide chains as they grow through the membrane. [ABSTRACT FROM AUTHOR]

Application of the two-dimensional polyacrylamide gel electrophoretic procedure recently described by Mets and Bogorad [4] to the resolution of Escherichia coli ribosomal proteins is described. This procedure is fast (running time of 8-10 h) and highly sensitive (1-2 µg protein per spot) and it gave good resolution for the majority of the 55 proteins in E. coli ribosomes. Moreover, the method has permitted the resolution of a large number of high-molecular-weight. proteins associated with ribosomes not exposed to high-salt washing. Using purified proteins, the positions in the electrophrogram of the individual proteins of the 30-S subunit have been determined. [ABSTRACT FROM AUTHOR]

In Escherichia coli cells infected with the bacteriophage MS2, pronounced inhibition of ribosomal RNA synthesis occurs amounting to 50% of that of the uninfected control cells at 30 min post-infection. Over the same period the synthesis of tRNA, mRNA and total protein remains close to the level of uninfected E. coli, yet the synthesis of host protein is gradually replaced by that of viral origin. After 30-35 min post-infection the macromolecular synthesis of all the types under study significantly decreases. It is suggested that suppression of host protein synthesis is caused not by selective inhibition at transcription or translation level, but is rather a result of competition between E. coil mRNA and MS2 RNA. On the other hand, exclusive suppression of only ribosomal RNA synthesis may arise from changes in the regulation of transcription of ribosomal RNA locus.

The homology between the 30-S ribosomal protein S1 and interference factor i has been investigated. The two proteins are indistinguishable by gel electrophoresis under various conditions. Similar peptides are obtained by cleavage with cyanogen bromide. After labelling with N-ethylmaleimide, enzymatic digestion yields homologous labelled peptides. This homology is confirmed by immunological data. Characteristic activities of the two proteins have been compared. Both bind polyuridylic acid and stimulate polypeptide synthesis on this template by S1-depleted ribosomes. Furthermore, S1 inhibits the translation of the coat protein cistron on MS2 RNA, while it has little effect on the overall translation of T4 mRNA, two characteristic properties of interference factor i. S1 and factor i are thus physically and functionally indistinguishable, which suggests that they have identical poly-peptide chains. Implications are discussed in terms of function.

1. L7 and L12 ribosomal proteins were reductively methylated in isolation and in situ, i.e. bound to the 50-S ribosomal subunit. The peptide bonds involving the carboxyl groups of &epsi-N-methylated lysines are resistant to trypsin attack. 2. Comparison shows that most of the lysine residues of' L7 and L12 proteins are more reactive in situ than in isolation. A partial unfolding or reduced association in situ is proposed. Notably when modified in solution, the reactivity of the acetylated form (L7) was greater than that of the deacetylated from (L12). 3. After reductive methylation the L7 and L12 proteins remain active in the GTPase reaction dependent on elongation factor G. [ABSTRACT FROM AUTHOR]

We have studied the evolution of ribosomal proteins over a spectrum of 13 species ranging from man to plants using a two-dimensional polyacrylamide gel electrophoresis technique. We tried to quantify the proximity of these species by coelectrophoresing the proteins from various combinations of two species. The following tentative conclusions have been reached. 1. For reptiles and birds which diverged 300 million years ago from the line leading to mammals, ribosomal proteins display the same fingerprints as mammals. 2. For amphibians and fish which diverged 350–400 and 440– million years ago respectively, the fingerprints show limited differences compared with mammals. Those of fish show some diversity within the species. 3. For lower species (crustaceans, molluscs) and plants, the fingerprints exhibit a great diversity. [ABSTRACT FROM AUTHOR]

A method is presented to isolate in pure form two acidic proteins, indicated as A1- and A2-protein from 50-S ribosomes of Escherichia coli. The advantage of this method is that it does not require prior isolation of subunits. The molecular weight of A1- and A2-protein was found by dodecylsulfate gel electrophoresis to be 11 500 with a maxum uncertainty of 1500. Sedimentation equilibrium centrifugation in 5 M guanidine hydrochloride indicates a molecular weight in the range of 12 000-13 000. The amino acid composition of the two proteins is remarkable and indistinguishable. A-protein has a high content of alanine and does not contain tyrosine, tryptophan, histidine or cysteine. On gel-electrofocusing the isoelectric points of A1- and A2-protein are slightly different, namely pH 4.7 and pH 4.85. The amount of A-protein in actively diving cells indicates that contrary to 30-S ribosomes, 50-S ribosomes have a restricted element of repeat. The number of copies of A-protein is found to be somewhat larger than two. [ABSTRACT FROM AUTHOR]

The 50-S ribosomal subunits were sedimented through 2 M LiCl or 3 M CsCl at low Mg2+ concentration (0.5-1 mM), and proteins in both pellet (cores) and supernatant (spilt proteins) were identified. No difference was detected between the two treatments: about, half of the proteins were found specifically in cores or in split fraction, while the other species (common proteins) were distributed in different proportions between the two fractions. This distribution behavior was shown to be due to dynamic exchange of proteins occurring between the core particles and the surrounding medium, By the double-labeling technique, the exchange of each protein was analyzed both in cores and in split fraction: this allowed us to estimate the partition coefficient of the common proteins. Furthermore, the analysis of the exchanges showed that the different common proteins approach at individual rates to the state of thermodynamic equilibrium in the test situation used (1 h incubation time). [ABSTRACT FROM AUTHOR]

The esterase activity of rat liver was mainly concentrated in the microsomal and nuclear fractions, with low activities in other fractions. On the basis of sensitivity to certain esterase inhibitors, the microsomal esterases were considered to be of a carboxylesterase type. The esterase distribution in sonicated rough microsomes, separated by zone centrifugation, was also investigated. Solubilization of the microsomal esterases was achieved by sodium deoxycholate, trypsin and phaspholipase-A treatment. Two esterases were solubilized from rat-liver microsomes by phospholipase-A treatment, and were fresher purified by chromatography on Sephadex G-100 and DEAE-cellulose. The enzymes were purified 256 and 154 times. The isoelectric points, Km values and molecular weights of the two esterases were determined. Both enzymes are of a carboxylesterase type. One of the esterase, however, was sensitive to HgCl2 of low concentrations, which is an unusual property for carboxylesterases. The question of whether the two enzymes constitute a monomer and a dimer of the same esterase or are completely different enzymes, is discussed. [ABSTRACT FROM AUTHOR]

50 S ribosomal subunits of Escherichia coli obtained by zonal centrifugation in B XV rotors were treated with various concentrations of LiCl in the absence and presence of urea. This treatment resulted in three protein fractions, each of which was subjected to CM-cellulose chromatography. Gel filtration in Sephadex G-100 (and preparative polyacrylamide electrophoresis) were used for further separation. The purity of the isolated proteins was better than 95% as shown by four methods. Proteins were isolated in yields of 6-90 mg depending mainly on the number and kind of purification steps. Instead of fractionation with LiCl prior to column chromatography, precipitation of extracted proteins at various concentrations of ammonium sulfate was tested. This method is useful if a given protein, e.g. from mutants is wanted in large quantity. [ABSTRACT FROM AUTHOR]

Particles of phage f2 formed in the presence of 5-azacytidine have nearly normal sedimentation coefficient and buoyant density, but their infectivity with respect to populations of normal phage is reduced. RNA extracted from these particles is partly degraded to small fragments and has very low template activity. Incorporation studies in vivo indicate that phage RNA-replicase can utilize both 5-azacytidine and 5-azauridine triphosphates for the synthesis of RNA. Phage RNA, however, contains much less 5-azacytosine than either replicative-form RNA or host RNA; apparently some secondary mechanism is operative, tending to eliminate plus-strands of RNA with high content of of 5-azacytosine from entering mature phage particles. Analyses of replicative-form RNA formed in cultures treated with 5-azacytidine show that this analogue is incorporated mostly instead of cytosine, but may also replace uracil quite frequently, apparently by incorrect base pairing. [ABSTRACT FROM AUTHOR]

1. 30S ribosomal subunits from Escherichia coli were hydrolyzed with ribonuclease T1, and the ribonucleoprotein fragments produced were fractionated on a 5% polyacrylamide/0.5% agarose composite gel. Two main breakdown products were observed corresponding in size to about 20% and 60% of the intact 30S particle. 2. Each fraction from the 5% composite gel was subjected to protein analysis on a periodatesoluble 15% polyacrylamide gel, run in the detergent Sarkosyl. The smaller ribonucleotprotein fragment was found to contain only four of the 30S ribosomal proteins, and these were present in equimolar amounts. The larger fragment had a complex protein composition; it was deficient in the four proteins contained in the smaller fragment, and was considerably enriched in the largest 30S protein. 3. The results show a striking correlation with Nomura's "assembly map" of the 30S particle. [ABSTRACT FROM AUTHOR]

1. The 43 S precursor of the 50 S ribosomal subunit shows a protein pattern very similar to that of a “core” particle derived from 50 S subunits on CsCl gradients. 2. A comparison of the protein patterns of “core” particles from 50 S subunits after CsCl equilibrium runs or incubation with increasing LiCl concentrations over the molarity range 0.4-6 M revealed that the proteins are successively released from the “core” in five distinct groups. 3. The protein pattern of the 21 S precursor of 30 S ribosomal subunits was compared with that of the reconstituted intermediate particle and LiCl-treated “core” particles of 30 S subunits. The 21 S is similar to both the reconstituted intermediate and the “core” particles derived by a 1 M LiCl treatment, whereas the reconstituted intermediate and this core particle differ rather more. [ABSTRACT FROM AUTHOR]

Phage M12 RNA, serving as a messenger for protein synthesis in vitro, is incorporated into polysomal structures containing up to ten ribosomes per RNA mlecule. If this RNA messenger is repressed by M12 coat protein prior to its translation, it binds a maximum of four ribosomes per RNA genome. This difference in polysome distribution is similar to the size difference between phage specific polysomes formed at early and late times of viral development in the infected from previous experiments in vitro, is also a major control mechanism of phage protein by synthesis in vitro. [ABSTRACT FROM AUTHOR]

An isokinetic gradient is a density and viscosity gradient, in which the particles during the centrifugation sediment with constant velocity. A numerical method for construction of isokinetic sucrose gradients for gradient centrifugation in B XIV zonal rotors is described, and several examples of gradients for separation of soluble proteins, nucleic acids, ribosomes and polysomes are given. The general usefulness of isokinetic gradients is illustrated by experimental separations of soluble immune complexes and of rat brain RNA. [ABSTRACT FROM AUTHOR]

A complex of rapidly labelled RNA and protein that can be liberated from polysomes by treatment with EDTA has been characterized in attempts to establish whether it is derived from the nuclear particles ("informofers") containing RNA of DNA-like nucleotide composition. After short time of labelling with [³H}orotic acid, polysomes were isolated, either by a method involving Triton X-100, or without any detergent ("free" polysomes). After treatment of polysomes with EDTA, the sedimentation rate of the rapidly-labelled RNA was considerably higher than that expected for pure RNA. OsCI density gradient centrifugation demonstrated that the buoyant density of the labelled material had a value intermediate between that of pure ENA and protein. Treatment with sodium deoxycholate or with 0.5 M KOl, increased considerably the buoyant density of the labelled material, while that of the ribosomal sub-units was only slightly affected. The results indicate that in polysomes the rapidly labelled RNA exists in a complex with protein that can be selectively removed by sodium deoxycholate or KCI. The proteins released by treatment with deoxycholate or with KCI were characterized by polyacrylamide gel electrophoresis. One of these proteins behaved similarly to the protein- component of the nuclear particle containing RNA of DNA-like base composition. It is suggested that this protein follows the rapidly labeiled RNA (presumably messenger RNA) during its transfer from the nucleus to the polysomes. [ABSTRACT FROM AUTHOR]

The labeling kinetics of rRNA in exponentially growing Tetrahymena pyriformis were analyzed quantitatively in order to determine pool-sizes and turnover rates of nuclear 17 and 25 S rRNA. The mathematical analysis of the system indicates that, during the steady state of growth, there is an inverse proportionality between pool-size and turnover rate of nuclear rRNA. Thus, from the labeling kinetics of rRNA and the growth rate constant (4.6 × 10-3 min-1), the pool-size of macronuclear 17 S rRNA was estimated at 0.5% of that of cytoplasmic 17 S rRNA corresponding to a turnover rate constant of 0.92 min-1 The analogues figures for 25 S rRNA were estimated at 1.6% and 0.29 min-1. Since the RNA content of macronuclei is about 2% of the cellular RNA content, it is concluded that during growth, most nuclear RNA is found in precursors of ribosomes and that macronuclei contain few, if any, finished ribosomes. Apart from its nsc on rRNA, the method described here may be generally useful in determining pool-sizes and turnover rates of other precursors, such as free ribosomal proteins. [ABSTRACT FROM AUTHOR]

A ribosome fraction enriched in "native" subunits by differential centrifugation yields, upon washing in a buffer containing ammonium chloride and magnesium ions, a protein mixture which can dissociate cytoplasmic ribosomes from Saccharomyces cerevisiae into 40 S and 60 S subunits. This heat dependent reaction cannot be related to any marked ribonuclease activity in the protein mixture. Furthermore, the mixture is unable to dissociate Escherichia coli or rabbit reticulocyte ribosomes; this property is unique, since proteolytic enzymes readily dissociate reticulocyte ribosomes as well as yeast ribosomes. Within 30 min of incubation, the factor-dependent dissociation reaches a plateau, due either to the stoichiometric mode of action of the factor, or to the inability of ribosomes to support complete dissociation under the ionic conditions of the experiments. These two points are discussed. [ABSTRACT FROM AUTHOR]

The metabolism and physical-chemical properties of nascent(precursor) 40 and 60 S sub-ribosomal particles have been studied in exponentially growing Tetrahymena pryrifomis GL. Analysis of formaldehyde-fixed 40 and 60S particles in isopyenic CsCl gradients reveals that they have a lower buoyant density than the corresponding 30 and 50 S ribosomal sub-units. More over, overall labeling of the cells with [3H]amino acid and [32P]phosphate shows that the precursor particles attain larger 3H/32P ratios than the corresponding sub-units, indicating that the precursor particles contain extra(accessory) protein that splits off when they are converted into ribosomal sub-units. The extra protein constitute 10 to 20 % of the total structure protein. Experiments in pulse-labeling with radioactive amino acids indicate that 40 and 60 S particles are very rapidly labeled. This suggests that, apart from the RNA moiety, at least parts of the structure ribosomal protein moiety associated with the nascent particles is newly synthesized. The possible involvement of 40 and 60 S particles in sub-unit exchange between rounds of translation was investigated by comparing their kinetics of labeling with that of the ribosomal sub-units. The results of the comparison indicate that the rate of recycling of ribosomal sub-units through the pool of 40 and 60 S particles is too slow account for sub-unit exchange between each round of translation. [ABSTRACT FROM AUTHOR]

Poly U-directed stimulation of preincubated calf lens ribosomes revealed that these particles from a mammalian source have a phenylalanine incorporation ability comparable to the Escherichia coli system. A search was made for optimal conditions. After variation of the magnesium concentration during preincubation two levels of maximal incorporation were observed. The region of highest relative stimulation did not coincide with these maxima. Preincubation under conditions of optimal amino acid incorporation yields 80S monomers and to a lesser extent 120S particles. No smaller units or breakdown products were observed in the analytical ultracentrifuge. Such particles could be demonstrated after prolonged dialysis of either polysomes or 80S monomers against 0.1 mM MgC12. Their sedimentation coefficients were 50S and 30S respectively but not 60 and 40 S. [ABSTRACT FROM AUTHOR]

Messenger ribonucleic acid was isolated from calf lens polyribosomes and fractionated. Previous identifications of the newly synthesized products have been extended in that the fidelity of the translation of the 14-S mRNA was assayed by fingerprinting analysis. The results suggest that lens messenger is translated with a high degree of fidelity in the cross systems even to the extent that the newly synthesized αA2 chains contain an acetylated methionine residue in the N-terminal position like the native chains. There seems to be no requirement for cell-specific protein factors in order to obtain accurate translation. Evidence is accumulating that the acetylation is not involved in the initiation mechanism. [ABSTRACT FROM AUTHOR]

We have designed a method for the large scale isolation of pure and highly active subunits from yeast cytoplasmic ribosomes. The method consists of the incubation of yeast, protoplasts in the presence of 1 mM NaN3. This causes the disappearance of polysomes and the formation of 80-S ribosomes that can be dissociated in 0.5 M KCl. In this way over 90% of the ribosomes can be dissociated into subunits. The subunits are isolated by centrifugation in a B-XV zonal rotor using an equivolumetric sucrose gradient. When this separation is performed at 5 °C, dimerization of 40-S particles to 65-S particles occurs and no pure subunits can be obtained, At 10 °C, there is no dimerization and the 60-S + 40-S subunits obtained are less than 1% cross-contaminated. In poly(U)-directed protein synthesis one subunit pair polymerizes phenylalanine residues at a rate of 1.7 residue per min. About 70% of the subunits were estimated to participate in this synthesis. Subunits prepared in the absence of dithiothreitol still bound phenylalanyltRNA, but, were inactive in phenylalanine polymerization. The 60-S subunits prepared without dithiothreitol were as active as those prepared in the presence of dithiothreitol when their peptidyltransferase activity was tested. [ABSTRACT FROM AUTHOR]

1. 30-S ribosomal subparticles were hydrolysed with ribonuclease T1 or pancreatic ribonuclease in the presence of 2 M urea. The RNA · protein fragments produced were separated on 5% polyacrylamide/0.50% agarose composite gels. Fractions from the composite gels were subjected to protein analysis on 17.5% periodate-soluble polyacrylamide gels run in the detergent sarkosyl, using the technique already published. 2. Several RNA · protein fragments were obtained by this procedure, each containing equimolar amounts of a few specific ribosomal proteins. Strict criteria for specificity of the proteins in each fragment were applied. Proteins S8 and S15 were found reproducibly in a small RNA · protein fragment, with only trace amounts of the remaining ribosomal proteins. Six proteins (S7, S9, S10, S13, S14, and S19) constitute another group, and fragments containing three, four, five, or all six of these proteins were observed. Protein S20 was occasionally associated with this group, or with S6, S16 or S17, and possibly S21. The latter (including S20) were also found in association with S8 and S15. 3. The individual proteins found in specific fragments are interpreted as being close neighbours in the 30-S particle. The fragment data can be incorporated into a re-arranged version of Nomura's "assembly map". [ABSTRACT FROM AUTHOR]

A protein kinase specifically associated with the ribosomal fraction has been isolated from rainbow trout testis. The enzyme was extracted from isolated trout-testis ribosomes in 0.6 M KCl, and was separated from trout testis protamine kinase by hydroxylapatite chromatography. The ribosomal protein kinase is a Mg2+-dependence enzyme that will transfer the terminal phosphoryl group from ATP into O-phosphoseryl linkages of the substrate. The enzyme will catalyze the phosphorylation of several basic proteins, and the slightly lysine-rich histone IIb2 is most readily phosphorylated followed by protamine and ribosomal proteins. Histones I, IIb1, and III are phosphorylated at an intermediate rate, while the arginine-rich histone IV and a acidic protein such as phosvitin are poor substrates. The enzyme is stimulated by the addition of dithiothreitol, and cyclic AMP enhances enzyme activity between 10 and 25%. [ABSTRACT FROM AUTHOR]