Misactivation of multiple starvation responses in yeast by loss of tRNA modifications.

Roland Klassen,Teresa Laguna,Alexander Bruch,Falk Butter,Raffael Schaffrath

doi:10.1093/nar/gkaa455

Abstract

Previously, combined loss of different anticodon loop modifications was shown to impair the function of distinct tRNAs in Saccharomyces cerevisiae. Surprisingly, each scenario resulted in shared cellular phenotypes, the basis of which is unclear. Since loss of tRNA modification may evoke transcriptional responses, we characterized global transcription patterns of modification mutants with defects in either tRNAGlnUUG or tRNALysUUU function. We observe that the mutants share inappropriate induction of multiple starvation responses in exponential growth phase, including derepression of glucose and nitrogen catabolite-repressed genes. In addition, autophagy is prematurely and inadequately activated in the mutants. We further demonstrate that improper induction of individual starvation genes as well as the propensity of the tRNA modification mutants to form protein aggregates are diminished upon overexpression of tRNAGlnUUG or tRNALysUUU, the tRNA species that lack the modifications of interest. Hence, our data suggest that global alterations in mRNA translation and proteostasis account for the transcriptional stress signatures that are commonly triggered by loss of anticodon modifications in different tRNAs.

Highlights

In all domains of life, tRNAs are subject to extensive posttranscriptional modification ranging from simple methylations to complex nucleobase side chain additions [1]
We further demonstrate that improper induction of individual starvation genes as well as the propensity of the tRNA modification mutants to form protein aggregates are diminished upon overexpression of tRNAGlnUUG or tRNALysUUU, the tRNA species that lack the modifications of interest
Transcriptome reprogramming in response to loss of different tRNA modifications Previous work established that composite tRNA modification mutants display common growth phenotypes and morphological aberrations, which can be attributed to malfunction of distinct tRNA species, i.e. tRNALysUUU and tRNAGlnUUG [2,16,20,21,47]

Summary

Introduction

In all domains of life, tRNAs are subject to extensive posttranscriptional modification ranging from simple methylations to complex nucleobase side chain additions [1] While these chemical modifications can be distributed all over the tRNA, the anticodon stem loop (ASL) represents a modification hotspot [1]. ASL nucleosides at position 37 or 34 can be modified by complex chemical side chains which help maintain the open loop configuration by preventing canonical base pairing (position 37) or enhance codon interaction (position 34 and 37). One of these ASL modifications, 5-methoxycarbonylmethyl-2-thiouridine at position 34 (mcm5s2U34) is added to tRNALysUUU, tRNAGlnUUG and tRNAGluUUC by two partially independent pathways in Saccharomyces cerevisiae. Loss of mcm5U34 or s2U34 alone or in combination causes various translational defects, including reduced ribosomal A-site binding, enhanced ribosome pausing at critical codons and ribosomal frameshifting

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Results

Conclusion