Methylation of tRNA by normal mouse liver and Erhlich ascites cell extracts

When Erhlich ascites tumor and normal mouse liver extracts were incubated with [3H-CH3]-S-adenosylmethionine and E. coli tRNA, the tumor extracts had a ten-fold higher methyltransferase activity than mouse liver extracts. However, only a two-fold higher methyltransferase activity was observed when methyl deficient mouse liver tRNA was used as a substrate. DEAE-Sephadex chromatography of alkaline hydrolysates of methyl deficient mouse liver tRNA (tRNA isolated from mice treated with ethionine) showed 70% of the 3H-methyl groups in the mononucleotide peak and 30% in alkaline stable di-, tri- and oligonucleotide peaks demonstrating methylation of both the base and ribose moieties. Perchloric acid digest of material isolated from the di-, tri- and oligonucleotide peaks confirm that the 3H-methyl groups are on the ribose moieties. In hydrolysates of E. coli tRNA 3H-methyl groups appeared in only the mononucleotide peak, i.e. only base methylation. These data, from Erhlich ascites cells, suggest that ribose methyltransferases may have greater RNA substrate specificity than the base methyltransferases and may act processively to produce alkaline stable oligonucleotides