Multiple forms of lysyl-transfer ribonucleic acid synthetase in Escherichia coli

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Abstract
Lysyl RNA tRNA synthetase (EC 6.1.1.6) was identified as 4 polypeptide spots after 2-dimensional polyacrylamide gel electrophoresis of whole-cell lysates of E. coli. Identification was made by migration with partially purified enzyme preparations, by peptide map patterns, by mutant analysis and by correlation of spot intensities with changes in enzyme levels under different growth conditions. Wild-type cells growing at 37.degree. C in glucose minimal medium displayed the enzyme predominantly as 2 spots (spots I and III). Growth at 46.degree. C, growth in the presence of alanine or glycyl-L-leucine, or growth of a strain with a mutational deficiency in S-adenosylmethionine synthetase (metK) greatly increased the synthesis of 2 other spots (spots II and IV). Polypeptides I and III, but not polypeptides II and IV, had altered isoelectric points in a lysyl-RNA synthetase mutant. Multiple forms of lysyl tRNA synthetase exist in vivo and they may be encoded by more than 1 gene.