Heat stress promotes pre-tRNA capping to modulate cap-dependent translation in Saccharomyces cerevisiae

Methylguanosine capping, a post-transcriptional modification of the 5' terminus of RNA polymerase II transcripts, influences RNA function, stability, and protein synthesis. Previously, we identified the cap modification in specific transfer RNA (tRNA) precursors (pre-tRNAs) transcribed by RNA polymerase III in Saccharomyces cerevisiae, and demonstrated that pre-tRNA capping prevents 5' exonucleolytic degradation of pre-tRNAs. Herein, we comprehensively mapped pre-tRNA capping and found that nearly all pre-tRNAs undergo cap modification. This analysis enabled precise determination of transcription start sites for all tRNA genes, and the capping efficiency was strongly influenced by the base-pairing probability between 5' leaders and 3' trailers of pre-tRNAs. Furthermore, pre-tRNA capping was significantly upregulated under heat stress, resulting in capped pre-tRNA-derived fragments. Capped pre-tRNAs modulated cap-dependent translation by sequestering eukaryotic initiation factor 4E (eIF4E). Overall, these findings suggest that pre-tRNA capping contributes to the regulation of cap-dependent translation under heat stress conditions in Saccharomyces cerevisiae.