RESTORATION OF AMINOACYLATION ACTIVITY OF UNDERMETHYLATED TRANSFER RNA BY IN VITRO METHYLATION

Undermethylated tRNA isolated from a RCrel mutant of Escherichia coli has been examined to determine whether its capacity to accept amino acids was comparable to that of normal tRNA from the same organism. Previously, little, if any differences have been reported (see Littauer and Milbauer, 1965; Borek and Srinivasan, 1966). In this communication we report the restoration of aminoacylation activity of undermethylated tRNA by in vitro methylation. In a mixture of undermethylated tRNAs2 2 Mixed undermethylated tRNAs are those tRNAs isolated from an RCrel mutant of E. coli after methionine starvation; i.e., a mixture of both normal and undermethylated species of tRNA (Mandel and Borek, 1961). from E. coli, we found that for four amino acids tested (Phe, Leu, Tyr, and His), the corresponding tRNAs showed decreased aminoacylation activities when compared to normal tRNA. Upon in vitro methylation of the undermethylated tRNAs with methylases free of RNase, an increase in the aminoacylation activities occurred. With two tRNA species (Phe and His), complete restoration of aminoacylation activity was observed. © 1968.