Journal
RNA
Volume 14, Issue 2, Pages 225-232Publisher
COLD SPRING HARBOR LAB PRESS, PUBLICATIONS DEPT
DOI: 10.1261/rna.859908
Keywords
tRNA splicing; RNA ligase; 2 '-phosphotransferase; translation; protein folding; mouse genetics
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Funding
- NIDDK NIH HHS [R01 DK047119, R37 DK047119, DK47119] Funding Source: Medline
- NIEHS NIH HHS [R01 ES008681, ES08681] Funding Source: Medline
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Unconventional mRNA splicing by an endoplasmic reticulum stress-inducible endoribonuclease, IRE1, is conserved in all known eukaryotes. It controls the expression of a transcription factor, Hac1p/XBP-1, that regulates gene expression in the unfolded protein response. In yeast, the RNA fragments generated by Ire1p are ligated by tRNA ligase (TrI1p) in a process that leaves a 2'-PO42- at the splice junction, which is subsequently removed by an essential 2'-phosphotransferase, Tpt1p. However, animals, unlike yeast, have two RNA ligation/repair pathways that could potentially rejoin the cleaved Xbp-1 mRNA fragments. We report that inactivation of the Trpt1 gene, encoding the only known mammalian homolog of Tpt1p, eliminates all detectable 2'-phosphotransferase activity from cultured mouse cells but has no measurable effect on spliced Xbp-1 translation. Furthermore, the relative translation rates of tyrosine-rich proteins is unaffected by the Trpt1 genotype, suggesting that the pool of (normally spliced) tRNA(Tyr) is fully functional in the Trpt1(-/-) mouse cells. These observations argue against the presence of a 2'-PO42- at the splice junction of ligated RNA molecules in Trpt1(-/-) cells, and suggest that Xbp-1 and tRNA ligation proceed by distinct pathways in yeast and mammals.
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