A tRNA-specific function for tRNA methyltransferase Trm10 is associated with a new tRNA quality control mechanism inSaccharomyces cerevisiae

Abstract

InSaccharomyces cerevisiae, a single homolog of the tRNA methyltransferase Trm10 performs m1G9 modification on 13 different tRNAs. Here we provide evidence that the m1G9 modification catalyzed byS. cerevisiaeTrm10 plays a biologically important role for one of these tRNA substrates, tRNATrp. Overexpression of tRNATrp(and not any of 38 other elongator tRNAs) rescues growth hypersensitivity of thetrm10Δstrain in the presence of the antitumor drug 5-fluorouracil (5FU). Mature tRNATrpis depleted intrm10Δcells, and its levels are further decreased upon growth in 5FU, while another Trm10 substrate (tRNAGly) is not affected under these conditions. Thus, m1G9 inS. cerevisiaeis another example of a tRNA modification that is present on multiple tRNAs but is only essential for the biological function of one of those species. In addition to the effects of m1G9 on mature tRNATrp, precursor tRNATrpspecies accumulate in the same strains, an effect that is due to at least two distinct mechanisms. The levels of mature tRNATrpare rescued in thetrm10Δmet22Δstrain, consistent with the known role of Met22 in tRNA quality control, where deletion ofmet22causes inhibition of 5′–3′ exonucleases that catalyze tRNA decay. However, none of the known Met22-associated exonucleases appear to be responsible for the decay of hypomodified tRNATrp, based on the inability of mutants of each enzyme to rescue the growth of thetrm10Δstrain in the presence of 5FU. Thus, the surveillance of tRNATrpappears to constitute a distinct tRNA quality control pathway inS. cerevisiae.