Talk abstracts
Talk on Saturday 09:30-09:45am submitted by William Marshall
Export, accumulation and degradation of 5’ end-extended, spliced tRNAIleUAU in yeast
William A Marshall (Molecular Genetics, Ohio State University), Kunal Chatterjee (Biology, Wittenberg University), Anita K Hopper (Molecular Genetics, Ohio State University)
Abstract:
The export of tRNA from the nucleus to the cytoplasm is an essential process that is integrally involved in cellular metabolism, aging, response to stress, and more. As transcribed, pre-tRNA contains extra leader and trailer sequences at the 5’ and 3’ ends, respectively. Normally, removal of the leader and trailer sequences occurs before tRNA is exported from the nucleus to the cytoplasm. However, 5’ end-extended spliced tRNA (aberrant tRNA) has been detected in yeast, indicating that tRNA was prematurely exported, since splicing of tRNA occurs in the cytoplasm at the surface of the mitochondria in S. cerevisiae. Aberrant tRNA cannot participate in translation, as the 3’ trailer prevents CCA addition and amino acid charging. We report that Mex67, but not the primary tRNA exportin Los1 or the newly bona fide tRNA exporter Crm1, exports the aberrant tRNA precursor. We also learned that two members of the 3’ to 5’ RNA exosome, Dis3 and Rrp6, function in reducing pools of the aberrant tRNA. While Dis3 is active in both the cytoplasm and the nucleus, Rrp6 is restricted to the nucleus, so aberrant tRNA must be reimported from the cytoplasm to be turned over in an Rrp6-dependent fashion, underscoring the role of the tRNA retrograde pathway in tRNA quality control. Also, members of the 5’ to 3’ rapid tRNA decay (RTD) pathway, Rat1 and Xrn1, do not function in turnover of this 5’ extended aberrant tRNA, perhaps because the 5’ extension on aberrant tRNA contains a cap or triphosphate that protects the tRNA from the RTD. Further studies are needed to determine whether 5’ extended tRNA that co-purifies with Mex67-Mtr2 is capped, as well as how 3’ trailer sequences or modifications at individual nucleotides could impact export, accumulation, and degradation of tRNA.
References:
Kilchert C, Wittmann S, Vasiljeva L. The regulation and functions of the nuclear RNA exosome complex. Nat Rev Mol Cell Biol. 2016 Apr;17(4):227-39. doi: 10.1038/nrm.2015.15. Epub 2016 Jan 4. PMID: 26726035.
Kramer EB, Hopper AK. Retrograde transfer RNA nuclear import provides a new level of tRNA quality control in Saccharomyces cerevisiae. Proc Natl Acad Sci U S A. 2013 Dec 24;110(52):21042-7. doi: 10.1073/pnas.1316579110. Epub 2013 Dec 2. PMID: 24297920; PMCID: PMC3876269.
Ohira T, Suzuki T. Precursors of tRNAs are stabilized by methylguanosine cap structures. Nat Chem Biol. 2016 Aug;12(8):648-55. doi: 10.1038/nchembio.2117. Epub 2016 Jun 27. PMID: 27348091.
Keywords: tRNA, Export, turn over