Search

Lists titles of research papers on biochemistry. "Redox control of catalysis in ATP-citrate lyase from rat liver"; "Construction and molecular dynamics of a soluble, enzymatically active form of the Escherichia coli penicillin-binding protein 5 and purification by dye chromatography"; "Studies on the variants of the protein toxins ricin and abrin".

Presents several forthcoming papers published on the December 1, 1983 issue of the "European Journal of Biochemistry." "Purification and Properties of a Thiol Protease From Rat-Liver Nuclei"; Changes in Proteoglycan Compositiion of F9 Teratocarcinoma Cells Upon Differentiation"; "Supercoiling and the Mechanism of Restriction Endonucleases"; Identification of the Gene for DNA Helicase II of Escherichia Coli."

Presents several articles to be published in the "European Journal of Biochemistry." "An Endonuclease From Yeast Mitochondrial Fractions," by R. Morosoli and C. V. Lusena; "Antigenic Relationships Between Pore Proteins of Escherichia coli K12," by N. Overbeeke, G. van Scharrenburg and B. Lugtenberg; "Respiratory Properties of Cytochrome-c-Deficient Mutants of Azotobacter vinelandii," by P.S. Hoffman, T. V. Morgan and D. V. DerVartanian; "Hydroxyl-Ion-Induced Subunit Dissociation of Yeast Cytoplasmic Pyruvate Decarboxylase. A Circular Dichroism Study," by R. F. W. Hopmann; Others.

This article presents information on forthcoming papers on biochemistry, to be published in the periodical "European Journal of Biochemistry." The papers include "Expression in Escherichia Coli of a Secreted Invertebrate Ferritin," by Matthias von Dart, Pauline M. Harrison and Werner Bottke, "Regulation of Protein Kinase A Subunits During Germination of Mucor Rouxii Sporangiospores," by Silvia Rossi and Silvia Moreno and "Optical Spectrum of Myeloperoxidase — Origin of the Red Shift," by René Plans, Younkyoo Kim, Gerald T. Babcock and Ron Wever.

Presents several forthcoming papers to be published in the "European Journal of Biochemistry." "Molecular Properties of Two Mutant Species of the Elongation Factor Tu" by P. H. van der Meide, F. J. Duisterwinkel, J. M. de Graaf, B. Kraal, L. Bosch, J. Douglass and T. Blumenthal; "The Mechanism of Uncoupling by Picrate in Escherichia coli K-12 Membrane System," by M. Michels and E. P. Bakker; "Nucleotide Sequence for a Novel Dunk Alpha-Globin Gene," by G. V. Paddock and J. Gaubatz; "Studies on the Actomyosin ATPase and the Role of the Alkali Light Chains," by B. Pope, P. D. Wagner and A. G. Weeds.

The paper presents various articles, which are to be published in the future issues of the European Journal of Biochemistry. Some of the articles to be published are — "Mechanisms for Albumin-Mediated Membrane Damage," by D. Dramas, E. Harvey, Al Lawrence and A. Thomas, "Transfer RNA Precursors Are Accumulated in Escherichia Coli in the Absence of RNase E," by B.K. Ray and D. Apirion, "A New Procedure for the Simultaneous Large-Scale Purification of Bacteriophage-T4-Induced Polynucleotide Kinase, DNA Ligase, RNA Ligase and DNA Polymerase," by G.M. Dolganov, A. V. Chestukhin and M.F. Shemyakin.

Lists papers to be published in the "European Journal of Biochemistry" after January 1987. "Expression of bovine pancreatic ribonuclease A in Escherichia coli," by K.P. Nambiar, et al; "Phenobarbital-mediated modulation of gene expression in rat liver — Analysis of cDNA clones; "Complete amino-acid sequence of the natural ATPase inhibitor from the mitochondria of the yeast Candida utilis.

Presents a list of articles to be published in the "European Journal of Biochemistry." "Cooperative Effects in the Peptidyltransferase Center of Escherichia Coli Ribosomes," by S. B. Bourd, M. K. Kukhanova, B. P. Gottikh; "Distribution of Secondary Structure Along the Fibronectin Molecule," by S. Yu. Venyaminov, M. L. Metsis, M. A. Chernousov and V. E. Koteliansky; "Chromatin Structure in Barley Nuclei," by G. Mithieux and B. Roux.

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]

`The O9-specific mannan of Escherichia coil was synthesized in vitro from GDP-[14C]mannose by membranes which were obtained from a phosphomannose isomerase-less mutant of E. coli O9:K29- :H-, Subsequent treatment of the membranes with dilute acid liberated a neutral product, whereas with aqueous phenol a charged product was obtained. Chromatography on DEAE-cellulose, incubation with alkaline phosphatase and microdetermination showed that the charged mannan was substituted with one phosphate per chain. The neutral 14C-labelled product of the incubation hr vitro was reduced with sodium boro[³H]hydride. After total acid hydrolysis, the radioactive material was chromatographed on paper in the presence of borate. It was found that [³H]glucitol, but no [³H, 14C]mannitol was present. When the neutral product, which was obtained after incubation of 14C-prelabelled membranes with nonradioactive GDP-mannose, was hydrolyzed with and without prior reduction with non-radioactive sodium borohydride, in subsequent paper chromatography, [14C]glucitol or [14C]glucose was found. The glucose was also converted enzymatically to gluconic acid, which was identified by paper electrophoresis. These results show that in the neutral O9-specific mannan glucose is at the reducing end and they indicate that the mannan chain grows at the non-reducing end. This is discussed with respect to the overall mechanism of the biosynthesis of the 09 antigen. [ABSTRACT FROM AUTHOR]

Lipopolysaccharides from a number of mutants of Escherichia coil K-12 were investigated by means of chemical and serological methods. Inhibition of passive hemagglutination and inhibition of precipitation show that L-rhamnose is the immunodominant sugar in the lipopolysaccharide from wild-type E. coli K-12. The disaccharide rhamnosyl-KDO (where KDO is 3-deoxy-D-manno-octulosonic acid) was isolated and characterized after mild acid hydrolysis of the lipopolysaccharide. It is concluded that rhamnose is present in the innermost part of the core as a side-chain substituent on KDO. From crosses between an E. coli K-12 donor and E. coil O8, hybrids were obtained which contained either one or both of the donor rfa and rfb clusters. Serum absorption studies with lipopolysaccharides from these hybrids indicated that the histidine-linked rfb cluster is responsible for the presence of rhamnose in the K-12 core oligosaccharide. Using paper chromatography of 32p-labelled lipopolysaccharides we have found heterogeneous lipopolysaccharide in two strains as well as some differences between two wild-type strains. The latter difference is believed to be due to varying contents of KDO-linked ethanolamine phosphate. The overall results presented together with those described in the companion paper clearly show that the core oligosaccharide in E. coil K-12 has a structure different from the types previously described for other strains of E. coli (designed coli R1 to coil R4). [ABSTRACT FROM AUTHOR]

A subset of the spin systems assigned in the ¹H NMR of the trp repressor in the first paper in this series (our penultimate preceding paper in this journal) can be identified as surface or buried residues on the basis of four independent types of measurement: (a) selective spin-lattice relaxation times; (b) the dependence of line widths on temperature and the concentration of manganous ion; (c) fluorescence quenching; and (d) titration behaviour. Criteria are developed for distinguishing surface and buried residues. The significance for the function of DNA biding proteins is 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 results presented in this paper establish relationships between structural morphological and functional properties of cytoplasmic membrane vesicles isolated from an Escherichia coli unsaturated fatty acid auxotroph. The membranes were isolated from cells grown in the presence of either oleic, linoleic, linolenic or elaidic acids. High-angle X-ray diffraction studies show that the order-disorder transitions induced by temperature variations and associated with the paraffin chains of the lipids are a function of the fatty acid composition of the membranes. In some cases "cocrystallization" of various lipid species takes place within a single type of ordered domains. In other cases there is segregation of various lipid species into more than one distinct type of ordered domain. The various order-disorder transitions observed induce morphological changes in the hydrophobic core of the membranes which can be detected by freeze-etch electron microscopy. A random distribution of particles on the fracture faces is observed when the paraffin chains of the lipids are disordered. Upon ordering of the paraffin chains, particles are excluded from the ordered domains and as a consequence, smooth areas and areas with densely packed particles are observed. The ratio of the smooth surface to particulated surface is proportional to the amount of ordered paraffin chains present. Moreover, the size of the smooth domains is a function of the fatty acid composition of the membranes. Discontinuities in the rate of D-lactate-dependent proline uptake as a function of temperature correlate with the order-disorder transitions observed. The high energies of activation at low temperatures are attributed to decreased mobility of the carrier proteins upon aggregation. In contrast, phosphoenolpyruvate-dependent vectorial phosphorylation does not respond to the ordering of the paraffin chains. [ABSTRACT FROM AUTHOR]

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]

We have determined the solution structures and examined thc dynamics of the Escherichia coli trp repressor (a 25-kDa dimer), with and without the co-repressor L-tryptophan, from NMR data. This is the largest protein structure thus far determined by NMR. To obtain a set of data sufficient for a structure determination it was essential to resort to isotopic spectral editing. Line broadening observed in this molecular mass range precludes for the most part the measurement of coupling constants and stereospecific assignments, with the inevitable result that the attainable resolution of the final structure will be somewhat lower than the resolution reported for smaller proteins and peptides. Nevertheless the general topology of the protein can be deduced from the subsets of NOEs defining the secondary and tertiary structure, providing a basis for further refinement using the full set of NOEs and energy minimization. We report here (a) an intermediate resolution structure that can be deduced from NMR data, covalent, angular and van-der-Waals constraints only, without resort to detailed energy calculations, and (b) the limits of uncertainty within which this structure is valid. An examination of trinse structures combined with backbone amide exchange data shows that even at this resolution three important conclusions can be drawn: (a) the protein structure changes upon binding tryptophan; (b) the putative DNA binding region is much more flexible than the core of the molecule, with backbone amide proton exchange rates 1000 times faster than in the core; (c) the binding of tryptophan stabilizes the repressor molecule, which is reflected in both the appearance of additional NOEs, and in the slowing of backbone proton exchange rates by factors of 3-10.Sequence-specific ¹H-NMR assignments and the secondary structure of the holopressor (L-tryptophan-bound form) have been reported previously [C. H. Arrowsmith, R. Pachter, R. B. Altman, S. B. Iyer & O. Jardetzky (1990) Biochemistry 29, 6332-6341]. Those for the trp aporepressor (L-tryptophan-free form), made using the same methods and conditions as described in the cited paper, are reported here. The secondary structure of the aporepressor was calculated from sequential and medium-range NOEs and is the same as reported for the holorepressor except that helix E is shorter. The tertiary solution structures for both forms of the repressor were calculated from long-range NOE data. The two structures are quite similar in overall topology to one another as well as to published crystal structures; however, the DNA binding region appears to be more disordered in solution than in the crystal structures. We propose that the greater flexibility of the DNA binding region observed by us as well as by others [C. L. Lawson, R.-G. Zhang, R. W. Schevitz, Z. Otwinowski, A. Joachimiak & P. B. Sigler (1988) Proteins 3, 18] plays an important role in the mechanism of DNA binding. [ABSTRACT FROM AUTHOR]

Prourokinase is a plasminogen activator of 411 amino acids which displays a clot-lysis activity through a fibrin-dependent mechanism, and which seems to be a promising agent for the treatment of acute myocardial infarction. The preparation of recombinant prourokinase in bacteria has been hampered by its insolubility and by difficulty in refolding the polypeptide chain. In this paper we describe the renaturation process of two recombinant proteins expressed in Escherichia coli as inclusion bodies: prourokinase and a deletion derivative (Δ125-prourokinase) in which 125 amino acids of the N-terminal region have been removed. Deletion of this sequence brings to higher refolding yields and faster kinetics (first-order rate constant of renaturation of 0.57 h-1 for Δ125-prourokinase and 0.25 h-1 for prourokinase). Our process involves sequential steps of denaturation, reduction and controlled refolding of the polypeptide chain. When applied to pure. non-glycosylated and active prourokinase, it gives a refolding yield of about 80%, demonstrating the efficiency of the renaturation procedure. Lower yields (15% and 30%, respectively, for prourokinase and Δ125-prourokinase) were obtained when the same refolding protocol was applied to inclusion bodies from bacteria. After purification to homogeneity (as shown by HPLC and SDS/PAGE) specific activities were 160000 and 250000 IU/mg protein, respectively, for prourokinase and Δ125-prourokinase. As with prourokinase, the deletion mutant 41 25-prourokinase displays a zymogenic nature, being activated by plasmin to the active two-chain form; however, this mutant is approximately fourfold more resistant than prourokinase to plasmin activation, and consequently shows a different fibrinolytic profile. [ABSTRACT FROM AUTHOR]

This paper reports the purification and characterization of a thioredoxin system (thioredoxin, thioredoxin reductase, NADPH) from the facultative phototroph Rhodobacter sphaeroides Y. Rhodobacter sph. Y thioredoxin was purified to homogeneity with an assay based on the reduction of 5,5′-dithiobis(2-nitrobenzoic acid) by NADPH and Escherichia coli thioredoxin reductase. Rhodobacter sph. Y thioredoxin reductase was purified with the same assay using NADPH and E. coli thioredoxin. Rhodobacter sph. Y thioredoxin contained 102 amino acid residues and had a single disulfide bond. The two half-cystine residues are part of the active site made up of the sequence -Ala-Glu-Trp-Cys-Gly-Pro-Cys-Arg- which is identical to that of E. coli thioredoxin except for the presence of an Arg instead of a Lys. Rhodobacter sph. Y thioredoxin contains two tryptophan residues. The fluorescence intensity of the tryptophan residues is quenched in oxidized thioredoxin; on reduction, a much smaller increase is observed with Rhodobacter sph. Y thioredoxin than with the E. coli protein. However, the presence of 5 M guanidine · HCl results in the complete exposure of the two tryptophan residues. Rhodobacter sph. Y thioredoxin reductase has structural and functional similarities to E. coli thioredoxin reductase; it has a molecular mass of 68 kDa, and consists of two, probably identical, subunits. Each subunit has one bound FAD molecule. The enzyme is highly specific for NADPH; it is also highly specific for Rhodobacter sph. Y thioredoxin with a Km value of 3.3 ± 0.6 µM. A kinetic study of the two thioredoxin systems shows that they have a high degree of cross-reactivity. [ABSTRACT FROM AUTHOR]

Penicillin-binding protein (pbp) 1b, the main DD-transpeptidase/transglycosylase of Escherichia coli, is normally present in the cell in three molecular forms α, β and γ, differenciated by their mobility in sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The three molecular forms are enzymatically active in vitro and their relative amounts are kept fairly constant in most labelling experiments with radioactive β-lactam antibiotics. In this paper, we have analyzed the expression of ponB (mrcB), the structural gone for pbp 1b, and the relation among the three forms of pbp 1b in ponB strains lysogenyzed by λ540 (ponB+) recombinant bacteriophages. Our data indicate that ponB is transcribed anti-clockwise on the E. coli chromosome and suggest that pbp 1bx is the first membrane-bound form of pbp 1b able to bind labelled β-lactams, and is the precursor of pbp 1bβ which is, in turn, the precursor of pbp 1bγ. [ABSTRACT FROM AUTHOR]

Enzyme-IIIgle is part of the glucose phosphotransferase system of Escherichia coli and Salmonella typhimturium and is phosphorylated by phosphoenolpyruvate in a reduction requiring enzyme 1 (phosphoeno/pyruvate-protein phospho- transferase), and the histidine-containing phospho-carrier protein HPr. In this paper we report the isolation of IIIgle from E. coil and the characterization of the activc center. Alkaline hydrolysis of [32P]P-IIIgle and chromatography of the hydrolysate suggested that the phosphoryl group is bound to a histidyl residue in P-IIIgle of S. typhimurium. Here we present 1H-NMR measurements of IIIgle and P-IIIgle from E. coli which further substantiate that the phosphoryl group in P-IIIgle is linked to the N-3 position of a histidyl residue. After phosporylation of IIIgle with [32P]Phosphoenolpyruvate, enzyme I and HPr, the phosphorylated protein was cleaved with either alkaline protease from Streptomyces griseus or subtilisin from Bacillus subtilis. According to amino acid analysis both proteases produced the same peptide carrying the phosphoryl group. The amino acid sequence of this peptide was found to be Val-His-Phe-Gly-Ile-Asp. The lower electrophoretic mobility of P-IIIgle on dodecylsulfute/polyacrylamide gels and its stronger binding to the hydrophobic matrix of a reversed-phase column compared to uuphosphorylated protein may indicate a structural change following phosphoenol/pyruvate-dependent phosphorylation. [ABSTRACT FROM AUTHOR]

Escherichia coli ribosomal proteins S4 and S17 were specifically labelled at their thiol groups with the acetylaminoethyl-dansyland/or bimane fluorophores. Each formed a complex with 16-S RNA and, when the other 30-S ribosomal proteins were added, a complete 30-S subunit with at least partial activity. If the 3′ end of the RNA was also labelled (with fluorescein) then the distance between the two fluorophores could be measured by Förster-type energy transfer. The result for S4 was 6.0 nm (60 Å) in the ribonucleoprotein complex and 5.6 nm (56 Å) in the 30-S subunit, and for S17 6.3 nm (63 Å) in the complex and 6.2 nm (62 Å) in the subunit. There is no evidence for a major change in the relative disposition of the 3′ and 5′ ends of the 16-S RNA during formation of the 30-S subunit. Sources of error are discussed, including the question of multiple labelling. In order to measure more accurately the extent of energy transfer a procedure based upon enzymic digestion was developed and is detailed in this paper. [ABSTRACT FROM AUTHOR]

After the recent investigation on the biochemical properties of the 2-keto-3-deoxy-gluconokinase and 2-keto-3-deoxy-6-phospho-gluconate aldolase in Escherichia coli K12, we report in this paper the induction mechanism of these two enzymes and the genetic control of a new enzymatic activity: the 2-keto-3-deoxy-gluconate transport system. The D-glucuronate and D-galacturonate raise the high basal levels of the kinase and aldolase on glycerol by a factor of 5 and 3-4, respectively, the kinase and aldolase being enzymes of the common degradative pathway of D-glucuronate and D-galacturonate. The differential rates of synthesis of these two enzymes are constant from the addition of the galacturonate. Under a variety of conditions (different inducers and substrates of growth) kinase and aldolase have been found to be synthesized non coordinately. The strongest decoordination is carried out by gluconate: this compound which is a good inducer of the aldolase, not only is unable to induce the kinase but also represses it. Moreover, the aldolase seems to be less sensitive to the catabolic repression than the kinase. By means of appropriate negative mutants we have established that the two hexuronates and two keto-uronates do not induce directly kinase and aldolase, but by sequential conversion into 2-keto-3-deoxy-gluconate. Furthermore, the fact that the hexuronates induce the kinase in aldolase-negative mutants (kdg A) and besides, "over" induce the aldolase in kinase negative mutants (kdg K) strongly suggests that, 2-keto-3-deoxy-gluconate is a true inducer for both enzymes. In addition, the gluconate which still induces the aldolase in an edd strain suggests that, this compound and/or the 6-phospho-gluconate are/is also inducer(s) of this enzyme. Moreover, we have isolated spontaneous mutants able to utilize the 2-keto-3-deoxy-gluconate as a unique carbon source. Two classes have been identified. The mutants of these classes which arise at high frequency (10-5 to 10-6) are either simultaneously constitutive for a specific 2-keto3-deoxy-gluconate transport system, kinase and aldolase (class kdg Rc) or only constitutive for the transport system (class kdg Pc). The 2-leto-3-deoxy-gluconate as exogenous substrate, which cannot induce its transport system in the wild type, behaves like a non-inducer substrate. So the strains kdg Rc and kdg Pc are respectively i- and oc lac-like mutants. These findings and the fact that we have found thermosensitive mutants mapping in the kdg R locus (34.5 min) and which are simultaneously derepressed for the permease, kinase and aldolase at 42 °C but not at 28 °C, strongly suggest that the synthesis of the three sequential enzymes degrading the 2-keto-3-deoxy-gluconate is negatively controlled by a common regulator gene product. The decoordinated syntheses of these three enzymes are in agreement with the scattering of the corresponding operons on the chromosome: transport system operon (76.5 min), kinase operon (69 min), aldolase operon (34 min). [ABSTRACT FROM AUTHOR]

1. 1. Acapsular (K-) forms were isolated from Escherichia colt strain E56b (serotype O8 :K27(A): H-). A number of different R strains were obtained from the K- forms by selection of spontaneous mutants and by phage selection. 2. The lipopolysaccharides of these R strains (consisting of core and lipid A) were subjected to mild acid degradation and, after removal of insoluble lipid A, the mixtures were fractionated by gel chromatography. Results of chemical analyses showed that the core oligosaccharides of different R mutants differed with respect to their sugar constituents as well as to the molar ratios of these constituents. A group of R mutants did not contain phosphate in their core oligosaccharides (P- mutants). Enzyme determinations indicated that one R mutant had a block involving UDP glucose pyrophosphorylase, whereas the enzymes of activation and interconversion of component sugars were intact in the other R mutants. 4. By allelic exchange (mating with S-form Hfr strains)it could be demonstrated that with one exception the chromosomal site of the S→ R mutation of all mutants maps close to mtl (mannitol utilization). In Salmonella the rfa locus maps fun the same region. All R mutants had an unimpaired (his-linked) rfb locus. 5. The groups of mutants which differed in the sugar composition of their core oligosaccharides could also be differentiated serologically and by their sensitivity to phages. There was serological cross reactivity between the lipopolysaccharides of some R mutants with R mutants of Salmonella minnesota which also have a very incomplete core. It is concluded that the lipopolysaccharides of the R mutants described in this paper have incomplete core structures which result from blocks at successive stages in the synthesis of the coli R1 core. in analogy to Salmonella these E. coli R mutants shoed, with one exception, be termed rfa type mutants. [ABSTRACT FROM AUTHOR]

Multiple species of Escherichia coli transfer RNA for valine and leucine were separated from each other by countercurrent distribution. Each transfer RNA species was charged with the corresponding radioactive amino acid and then allowed to transfer its label into hemoglobin peptides in the ribosomal system from rabbit reticulocytes. Earlier experiments had shown that the minor tRNAIIbLeu would only label one position, no. 48 of the α-hemoglobin chain under these conditions. In this paper we report the coding properties of the other separated leucine tRNAs and of multiple valine tRNAs with the hemoglobin messenger. The leucine codons in the α-chain messenger can be divided into three classes with respect to their tRNA response : (a) position 48 is recognized only by tRNAIIbLeu. (b) The majority of the leucine codons can be recognized by both the two major leucine tRNAs. (c) Some leucine codons can only be recognized by one of the major leucine tRNAs. Similarly, two classes of valine codons can be distinguished in the α-chain messenger. [ABSTRACT FROM AUTHOR]