tRNA: Splicing and Intron Turnover

In most eukaryotic genomes a subset of tRNA genes contains introns. Introns in tRNAs genes are short sequences located 1 nt. 3′ of the anticodon. Introns are removed from precursor tRNAs (pre‐tRNA) by a conserved heterotetrameric protein enzyme, tRNA splicing endonuclease (SEN), that recognizes pre‐tRNA structure rather than sequence motifs at splice junctions. In vertebrate cells intron removal from pre‐tRNAs occurs in the nucleoplasm; in contrast, pre‐tRNA splicing in budding yeast was surprisingly discovered to occur on the mitochondrial surface (Yoshihisa et al . 2003). We recently reported that the SEN complex also locates to the mitochondrial surface in fission yeast (Wan & Hopper 2018) and, therefore, pre‐tRNA splicing on the mitochondrial surface has been conserved for at least 500 million years. The mitochondrial outer membrane protein, Tom70, is required for efficient SEN subunit location to mitochondria in both budding and fission yeast (Wan & Hopper 2018). The freed introns are rarely detected in cells and until recently it was unknown how are they are turned over. We identified at least 5 separate, species‐specific mechanisms that function in tRNA intron destruction (Wu & Hopper, 2014; Bao, unpublished). Interestingly, under particular stress conditions, specific tRNA introns accumulate, possibly indicating their functions in stress response (Peltier, unpublished). Moreover, we discovered that tRNA introns possess long stretches of perfect complementarity to particular budding yeast mRNAs (Bao, unpublished), also indicative of their possible roles in gene regulation. Our initial experiments support the hypothesis that tRNA introns may function as a novel type of noncoding regulatory RNA (Nostramo, unpublished). Support or Funding Information NIH GMS 122884