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L S Williams

Publications and source records attributed to L S Williams.

At least 109 records · Page 6Linked to original sources
PubMed1978

Synthesis and activities of branched-chain aminoacyl-tRNA synthetases in threonine deaminase mutants of Escherichia coli.

Valyl-, isoleucyl-, and leucyl-tRNA synthetase activities were examined in an Escherichia coli K-12 strain that possessed a deletion of three genes of the ilv gene cluster, ilvD, A, and C, and in a strain with the same deletion that also carried the lambdadilvCB bacteriophage. It was observed that the branched-chain tRNA synthetase activities of both strains were considerably less than those of the normal strain during growth in unrestricted medium. Furthermore, during an isoleucine limitation, there was a further reduction in isoleucyl-tRNA synthetase activity and an absence of the isoleucine-mediated derepression of valyl-tRNA synthetase formation in both of these mutants, as compared with the normal strain. In addition, it was observed that these branched-chain synthetase activities were reduced in steady-state cultures of several ilvA point mutants. However, upon the introduction of the ilv operon to these ilvA mutants by use of lambda bacteriophage, there was a specific increase in the branched-chain synthetase activities to levels comparable to those of the normal strain. These results support our previous findings that the stability and repression control of synthesis of these synthetases require some product(s) missing in the ilvDAC deletion strain and strongly suggest this component is some form of the ilvA gene product, threonine deaminase.

Amino Acyl-tRNA Synthetases↗
PubMed1975

Regulation of branched-chain aminoacyl-transfer ribonucleic acid synthetases in an ilvDAC deletion strain of Escherichia coli K-12.

Valyl-, isoleucyl-, and leucyl-transfer ribonucleic acid synthetase formation was compared in isogenic strains of Escherichia coli K-12 that differed only in that one strain carried a deletion of three genes of the ilv gene cluster, ilvD, -A, and -C. It was found that: (i) the activities of these synthetases in the deletion strain were less than those in the normal strain during growth in minimal medium supplemented with excess isoleucine, valine, and leucine, and (ii) their stability was reduced in the deletion strain during specific branched-chain amino acid limitations. The results of density-labeling experiments suggest that the in vivo stability of valyl-, isoleucyl-, and leucyl-transfer ribonucleic acid synthetases requires some product missing in the ilvDAC deletion strain.

Amino Acyl-tRNA Synthetases↗
PubMed1974

Derepression of synthesis of the aminoacyl-transfer ribonucleic acid synthetases for the branched-chain amino acids of Escherichia coli.

The kinetics of derepression of valyl-, isoleucyl-, and leucyl-transfer ribonucleic acid (tRNA) synthetase formation was examined during valine-, isoleucine-, and leucine-limited growth. When valine was limiting growth, valyl-tRNA synthetase formation was maximally derepressed within 5 min, whereas the rates of synthesis of isoleucyl-, and leucyl-tRNA synthetases were unchanged. Isoleucine-restricted growth caused a maximal derepression of isoleucyl-tRNA synthetase formation in 5 min and derepression of valyl-tRNA synthetase formation in 15 min with no effect on leucyl-tRNA synthetase formation. When leucine was limiting growth, leucyl-tRNA synthetase formation was immediately derepressed, whereas valyl- and isoleucyl-tRNA synthetase formation was unaffected by manipulation of the leucine supply to the cells. These results support our previous findings that valyl-tRNA synthetase formation is subject to multivalent repression control by both isoleucine and valine. In contrast, repression control of iso-leucyl- and leucyl-tRNA synthetase formation is specifically mediated by the supply of the cognate amino acid.

Amino Acyl-tRNA Synthetases↗
PubMed1974

First enzyme of histidine biosynthesis and repression control of histidyl-transfer ribonucleic acid synthetase of Salmonella typhimurium.

The regulation of formation of histidyl-transfer ribonucleic acid (tRNA) synthetase was examined in strains of Salmonella typhimurium. When the first of the histidine-forming enzymes was wild type, the presence of 2-thiazolealanine in the growth medium prevented repression of histidyl-tRNA synthetase formation elicited by the addition of 1, 2, 4-triazole-3-alanine to these cultures. Conversely, thiazolealanine had no effect on repression of histidyl-tRNA synthetase formation by triazolealanine in hisG mutant strains. These data suggest a relationship between the control of histidyl-tRNA synthetase formation and the functional state of the histidine operon.

Amino Acids↗
PubMed1974

Regulation of synthesis of the branched-chain amino acids and cognate aminoacyl-transfer ribonucleic acid synthetases of Escherichia coli: a common regulatory element.

Regulation of isoleucine, valine, and leucine biosynthesis and isoleucyl-, valyl-, and leucyl-transfer ribonucleic acid (tRNA) synthetase formation was examined in two mutant strains of Escherichia coli. One mutant was selected for growth resistance to the isoleucine analogue, ketomycin, and the other was selected for growth resistance to both trifluoroleucine and valine. Control of the synthesis of the branched-chain amino acids by repression was altered in both of these mutants. They also exhibited altered control of formation of isoleucyl-tRNA synthetase (EC 6.1.15, isoleucine:sRNA ligase, AMP), valyl-tRNA synthetase (EC 6.1.1.9, valine:sRNA ligase, AMP), and leucyl-tRNA synthetase (EC 6.1.1.4, leucine:sRNA ligase, AMP). These results suggest the existence of a common element for the control of these two classes of enzymes in Escherichia coli.

Alcohol Oxidoreductases↗
PubMed1973

Evidence for the existence of two arginyl-transfer ribonucleic acid synthetase activities in Escherichia coli.

Two arginyl-transfer ribonucleic acid (tRNA) synthetase (EC 6.1.1.13, arginine: ribonucleic acid ligase adenosine monophosphate) activities were found in extracts of Escherichia coli strains AB1132 and NP2. The two arginyl-tRNA synthetase activities in extracts of strain AB1132 were found to be separable by diethylaminoethyl-cellulose column chromatography, Sephadex column fractionation, and by sucrose density gradient centrifugation. In addition, in the standard assay using extracts of strain AB1132 there were two pH optima for arginyl-tRNA synthetase activity. Furthermore, when arginyl-tRNA synthetase of strain NP2 was fractionated by hydroxylapatite column chromatography, two activities were observed which were similar to those of strain AB1132.

Amino Acyl-tRNA Synthetases↗
PubMed1973

Control of arginine biosynthesis in Escherichia coli: role of arginyl-transfer ribonucleic acid synthetase in repression.

The physiological role of arginyl-transfer ribonucleic acid (Arg-tRNA) synthetase (E.C. 6.1.1.13, arginine: RNA ligase adenosine monophosphate) in repression of arginine biosynthetic enzymes was examined. Mutants with nonrepressible synthesis of arginine biosynthetic enzymes were isolated from various strains of Escherichia coli by resistance to growth inhibition by canavanine, an arginine analogue. These mutants possessed reduced Arg-tRNA synthetase activities which were qualitatively different from the synthetase activity of the wild type. The mutant enzymes exhibited turnover in vivo and were less stable in vitro than the wild type at both 4 C and 40 C; they possessed different affinities for both arginine and canavanine as measured by the three common assay systems for aminoacyl-tRNA synthetases. Furthermore, in one case it was shown that (i) the mutant possesed unaltered uptake of arginine, and (ii) that the mutant possessed diminished ability to incorporate canavanine into proteins and to attach canavanine to tRNA. These observations suggested that the mutation to canavanine resistance involved a structural change in Arg-tRNA synthetase. Likewise, the results of genetic experiments suggested that the mutants differed from the wild-type strain at only one locus, and that this lies in the region of the chromosomes that includes a structural gene for Arg-tRNA synthetase. It appears that Arg-tRNA synthetase may be involved in some way in repression by arginine of its own biosynthetic enzymes.

Amino Acyl-tRNA Synthetases↗
PubMed1973

Control of arginine biosynthesis in Escherichia coli: characterization of arginyl-transfer ribonucleic acid synthetase mutants.

The arginyl-transfer ribonucleic acid (Arg-tRNA) synthetase (EC 6.1.1.13, arginine: RNA ligase adenosine monophosphate) mutants, exhibiting nonrepressible synthesis of arginine by exogenous arginine, were employed in studies of several biochemical properties. Two of these mutants possessed Arg-tRNA synthetases with a reduced affinity for arginine, and this enzyme of another mutant had a reduced affinity for arginine-tRNA (tRNA(arg)). The mutant possessing an Arg-tRNA synthetase with an altered K(m) for tRNA(arg) was found to have reduced in vivo aminoacylation of two of the five isoaccepting species of tRNA(arg) and complete absence of aminoacylation of one of the isoaccepting species.

Acylation↗
PubMed1973

Regulation of methionyl-transfer ribonucleic acid synthetase formation in Escherichia coli and Salmonella typhimurium.

The control of methionyl-transfer ribonucleic acid (tRNA) synthetase (l-methionine: soluble RNA ligase [adenosine monophosphate]) was studied in methionyl-tRNA synthetase mutants of Escherichia coli and Salmonella typhimurium. The results of activity determinations with crude extracts indicate that this enzyme of the E. coli mutant strain possessed a reduced affinity for methionine-tRNA, whereas this enzyme of the S. typhimurium mutant exhibited a decreased affinity for l-methionine. The differential rate of methionyl-tRNA synthetase formation in these two mutants was several-fold greater than that of the respective parental strains. On the other hand, the level of in vivo aminoacylation of methionine-tRNA was only about one-third that of the parent strains. These results suggest that aminoacylation of methionine-tRNA is a necessary step in repression control of methionyl-tRNA synthetase of both E. coli and S. typhimurium strains.

Amino Acyl-tRNA Synthetases↗
PubMed1973

Control of arginine biosynthesis in Escherichia coli: inhibition of arginyl-transfer ribonucleic acid synthetase activity.

In this study, we have extended our earlier observations indicating in vitro inhibition of arginyl-transfer ribonucleic acid synthetase (EC 6.1.13, arginine: soluble ribonucleic acid ligase, adenosine monophosphate) activity by the arginine biosynthetic precursors ornithine, citrulline, and argininosuccinate. Furthermore, we report evidence which suggest that this enzyme activity is inhibited by these arginine precursors in vivo and that this inhibition of activity results in a derepression of arginine biosynthesis.

Amino Acyl-tRNA Synthetases↗
PubMed1972

Role of histidine transfer ribonucleic acid in regulation of synthesis of histidyl-transfer ribonucleic acid synthetase of Salmonella typhimurium.

The role of histidine transfer ribonucleic acid (tRNA) in repression of synthesis of histidyl-tRNA synthetase was examined in two strains of Salmonella typhimurium, one of which was a histidine tRNA (hisR) mutant possessing 52% of the wild-type (hisR(+)) histidine tRNA and a derepressed level of the histidine biosynthetic enzymes during histidine-unrestricted growth. Histidine-restricted growth caused a derepression of the rate of formation of histidyl-tRNA synthetase in both strains. In the case of the wild-type strain, addition of histidine to the derepressed culture caused a repression of synthesis of histidyl-tRNA synthetase for at least one generation of growth. In contrast, when histidine was restored to the derepressed hisR mutant culture, synthesis of histidyl-tRNA synthetase was continued at the initial derepressed rate. These results suggest that histidine must be attached to histidine tRNA for repression of synthesis of histidyl-tRNA synthetase.

Aerobiosis↗
PubMed1972

Regulation of synthesis of methionyl-, prolyl-, and threonyl-transfer ribonucleic acid synthetases of Escherichia coli.

Proline- and threonine-restricted growth caused a three- to fourfold derepression of the differential rate of synthesis of the prolyl- and threonyl-transfer ribonucleic acid (tRNA) synthetases, respectively. Similarly, there was approximately a 24-fold derepression in the rate of synthesis of methionyl-tRNA synthetase during methionine restriction. Addition of the respective amino acids to such derepressed cultures resulted in a repression of synthesis of their cognate synthetases. These results support previous findings and further strengthen the idea that the formation of aminoacyl-tRNA synthetases is regulated by some mechanism which is mediated by the cognate amino acids.

Aerobiosis↗
PubMed1972

Regulation of histidyl-transfer ribonucleic acid synthetase formation in a histidyl-transfer ribonucleic acid synthetase mutant of Salmonella typhimurium.

Control of formation of the histidyl-transfer ribonucleic acid (tRNA) synthetase with an increased K(m) for histidine was studied in a hisS mutant of Salmonella typhimurium. Histidine restriction of both the hisS and hisS(+) strains resulted in a derepression of synthesis of histidyl-tRNA synthetase. When grown in a concentration less than the K(m) (100 mug/ml) of l-histidine, the hisS mutant maintained a higher level of histidyl-tRNA synthetase than the hisS(+) strain. Addition of excess amounts of l-histidine to the growth medium of the hisS mutant culture grown with 100 mug of l-histidine per ml resulted in a repression of histidyl-tRNA synthetase formation to equal that of the hisS(+) strain grown in 100 mug of l-histidine per ml. These data confirm previous findings that histidine tRNA is involved in the repression of synthesis of histidyl-tRNA synthetase.

Amino Acyl-tRNA Synthetases↗