Abstract
Purified bulk tRNA from M. vannielii (C source, formate) showed variation in the modified nucleoside pattern reported for Escherichia coli as analyzed by ion-exchange and TLC. Ribothymidine and 7-methylguanosine were absent; 1-methyladenosine, 1-methylguanosine, N2-methylguanosine, N2,N2-dimethylguanosine, thiolated nucleosides, pseudouridine, dihydrouridine and O2''-methylcytidine were quantitated. In vitro methylation by M. vannielii extracts with S-adenosylmethionine and undermethylated E. coli tRNA revealed active tRNA methyltransferases for formation of methylated residues found in native M. vannielii tRNA, but none for the formation of 7-methylguanosine or ribothymidine. The native M. vannielii tRNA became methylated in the 7-methylguanosine position by E. coli extracts, but ribothymidine was not formed. Both M. vannielii and E. coli tRNA methyltransferases produced unidentified methylated residues in tRNA lacking or deficient in ribothymidine.

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