Thermally induced biosynthesis of 2'-O-methylguanosine in tRNA from an extreme thermophile, Thermus thermophilus HB27.

The contents of 2'-O-methylguanosine and 1-methyladenosine in unfractionated tRNA obtained from Thermus thermophilus HB27 were found to increase significantly when the bacterium was grown at a higher temperature (80 degrees C). S-Adenosyl-L-methionine-dependent tRNA (guanosine-2')-methyltransferase (EC 2.1.1.34) and tRNA (adenine-1)-methyltransferase (EC 2.1.1.36) were detected in a cell-free extract of the thermophile, and both of them were partially purified. tRNA (guanosine-2')-methyltransferase specifically catalyzed the methylation of the guanylate residue at position 19 from the 5' end of Escherichia coli tRNAMetf. The amounts of these methyltransferases in the cells and their thermal characteristics seemed to be independent of the growth temperature of the bacterial cells from which the enzymes were extracted. It was inferred that the temperature dependence of the methylation process in vivo is accounted for, not by temperature dependence of enzyme formation, but by that of the enzyme activity.