[tRNA methyltransferase activity in Escherichia coli growing on a medium with methionine and S-methylmethionine]

tRNA methylating enzymes isolated from E. coli 113-3 grown in a medium with methionine or S-methylmethionine differed in the activity of transfer of the 14CH3-group from 14CH3-S-adenosyl-L-methionine (SAM) to tRNA in the in vitro experiments in heterological systems consisting of tRNA methyltransferases from E. coli 113-3 and a substrate of methylation, viz. methyl-deficient tRNA isolated from E. coli K 12W6. In such a system, tRNA methyltransferases from E. coli 113-3 grown on S-methylmethionine methylated tRNA from E. coli K 12W6 at a rate almost twice as high as that in the case of the culture grown on methionine. At the same time, the activity of guanine methylation yielding 7-methylguanine increased significantly. The protein obtained after precipitation of cell-free extracts with ammonium sulfate was separated into four fractions using a system of columns packed with Sephadex G-25 and DEAE-cellulose. These fractions differed quantitatively in culture grown either on methionine or S-methylmethionine.