An intact unfolded protein response in Trpt1 knockout mice reveals phylogenic divergence in pathways for RNA ligation.
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 (Trl1p) in a process that leaves a 2'-PO4(2-) 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'-PO4(2-) 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.
Harding
Heather P
HP
Kimmel Center for Biology and Medicine of the Skirball Institute, New York University School of Medicine, New York, New York 10016, USA. harding@saturn.med.nyu.edu
Lackey
Jeremy G
JG
Hsu
Hao-Chi
HC
Zhang
Yuhong
Y
Deng
Jing
J
Xu
Rui-Ming
RM
Damha
Masad J
MJ
Ron
David
D
D000818:Animals; D004268:DNA-Binding Proteins / Q000235:genetics*; D005095:Exoribonucleases / Q000235:genetics / Q000378:metabolism*; D014644:Genetic Variation; D051379:Mice; D018345:Mice, Knockout; D009687:Nuclear Proteins / Q000235:genetics*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D014176:Protein Biosynthesis / Q000235:genetics*; D017510:Protein Folding; D022821:RNA Splice Sites / Q000235:genetics; D012326:RNA Splicing / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D012365:RNA, Transfer, Tyr / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D014443:Tyrosine / Q000378:metabolism; D000071717:X-Box Binding Protein 1
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D022821:RNA Splice Sites; D012333:RNA, Messenger; D012365:RNA, Transfer, Tyr; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605544:Xbp1 protein, mouse; D014443:Tyrosine; D017853:Phosphotransferases (Alcohol Group Acceptor); C527101:Trpt1 protein, mouse; D005095:Exoribonucleases; C029364:2'-phosphodiesterase