THE METHYLATION OF ONE SPECIFIC GUANOSINE IN A PRE-TRANSFER RNA PREVENTS CLEAVAGE BY RNASE-P AND BY THE CATALYTIC M1 RNA

Several modified nucleosides were introduced during in vitro RNA synthesis into a pre The pre tRNAser were used as substrates for RNase P enzymes. No effects were observed with biotin-8-ATP or [α-S]-GPT whereas with m7 the cleavage reaction was completely inhibited. Analysis of pre-tRNAs which contained m7 at various positions has revealed a single base at the 5′-end of the acceptor stem where this modification absolutely prevents cleavage by catalytic M1 RNA, eukaryotic and prokaryotic RNase P holoenzymes. These results suggest that a critical contact must be made between pre-tANA substrate and enzyme/ribozyme or that the approach of the potential cleaving agent (a positive magnesiumion) is made impossible by the positive charge at N-7 of the guanosine. in addition, we have shown that a pre-tRNA containing only M7G's can still form a complex with M1 RNA in a gel retardation assay. © 1990 Oxford University Press.