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

Abstract

InSaccharomyces cerevisiaea 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 decay of hypomodified tRNATrp, based on inability of mutants of each enzyme to rescue growth of thetrm10Δstrain in the presence of 5FU. Thus, the surveillance of tRNATrpappears to constitute a distinct tRNA quality control pathway inS. cerevisiae.

Diversity in Biological Function and Mechanism of the tRNA Methyltransferase Trm10

“…Interestingly, the trm10Δ strain exhibited the most severe growth defect when grown in 5FU compared to single deletion strains of other tRNA and rRNA modification genes (Figure ). Although a general negative effect on tRNA structure was implied by the original observations, subsequent studies in our lab have revealed that a single tRNA (tRNA Trp ) is responsible for the observed hypersensitivity to 5FU in the absence of Trm10 modification due to the extremely depleted levels of tRNA Trp , but not other Trm10 substrate tRNAs, in trm10Δ cells . We also showed that tRNA Trp abundance is already significantly decreased in trm10Δ cells even in the absence of 5FU, where viability is not impacted .…”

“…Although a general negative effect on tRNA structure was implied by the original observations, subsequent studies in our lab have revealed that a single tRNA (tRNA Trp ) is responsible for the observed hypersensitivity to 5FU in the absence of Trm10 modification due to the extremely depleted levels of tRNA Trp , but not other Trm10 substrate tRNAs, in trm10Δ cells . We also showed that tRNA Trp abundance is already significantly decreased in trm10Δ cells even in the absence of 5FU, where viability is not impacted . Thus, the impact of the Trm10 modification even in yeast is biologically significant despite the lack of an obvious growth defect in trm10Δ cells grown under standard laboratory conditions.…”

“…Similarly, of the 12 elongator tRNA species that Trm10 modifies in S. cerevisiae , only mature tRNA Trp lacking m 1 G9 modification undergoes quality control, providing another example of a tRNA modification that is present on multiple substrates in the cell but is seemingly only important for one tRNA . Interestingly, Trm10-dependent surveillance of tRNA Trp appears to be mediated by a new pathway that shares some, but not all, features with previously described tRNA quality control mechanisms . The identification of specific exonucleases that degrade tRNA lacking the m 1 G9 modification to cause the 5FU hypersensitive and synthetic temperature sensitive phenotypes associated with the gene in S. cerevisiae is an ongoing area of investigation, but our observations and those of the Phizicky lab should help to answer these questions about the diverse biological impacts of Trm10 in S. cerevisiae .…”

“…Yet, even among these 4 species, overexpression of only one of these, tRNA Val AAC , is able to rescue the temperature sensitivity of the double mutant strain, even though the three other tRNAs are also missing m 7 G46 and m 5 C49 modifications in the deletion strains . Similarly, of the 12 elongator tRNA species that Trm10 modifies in S. cerevisiae , only mature tRNA Trp lacking m 1 G9 modification undergoes quality control, providing another example of a tRNA modification that is present on multiple substrates in the cell but is seemingly only important for one tRNA . Interestingly, Trm10-dependent surveillance of tRNA Trp appears to be mediated by a new pathway that shares some, but not all, features with previously described tRNA quality control mechanisms .…”