SPECIFICITY OF TRANSFER RIBONUCLEIC ACID METHYLASES FROM RAT LIVER

Transfer ribonucleic acid (tRNA) methylating enzymes were isolated in high-speed supernatants from rat liver extracts and partially purified by DEAE-cellulose chromatography. The purified enzyme methylated guanine in the 2N position and adenine in the 1 position using Escherichia coli methyl-deficient tRNA as substrate and S-adenosylmethionine as the methyl donor. The tRNA could be methylated to an extent of more than 0.5 methylated base of each type per molecule. The question of whether the methylase recognizes a base by virtue of its surrounding nucleotide sequence was examined by fractionation of a pancreatic ribonuclease digest of l4C-methylated tRNA. Almost all of the radioactivity was found in two sequences, one of which was identified as adenylyl-(3′5′)2N-methylguanylyl-(3′,5′)-cytidylic 3′-acid and the other as an oligonucleotide containing methyl-adenine in a nonterminal position. © 1968, American Chemical Society. All rights reserved.