The tRNA N2,N2,-dimethylguanosine-26 methyltransferase encoded by gene trm1 increases efficiency of suppression of an ochre codon in Schizosaccharomyces pombe

In the majority of eukaryotic tRNAs, the guanosine at position 26 is modifi ed by a dimethyl group, but so far a function of this modification has not been detected. We isolated the Schizosaccharomyces pombe gene, trm1, encodi ng the tRNA N2,N2-dimethylguanosine-26 methyltransferase. Strains having th e gene deleted completely lack N2,N2-dimethylguanosine. In strains carrying the weak ochre tRNA suppressor sup3-i, deletion of trm1 abolishes suppress ion indicating that the tr ml deletion acts as an antisuppressor mutation. The result suggests that in vivo N2,N2-dimethylguanosine-26 increases the c apacity of the sup3-i serine tRNA to translate the UAA (ochre) codon. (C) 1 999 Federation of European Biochemical Societies.