The transmembrane kinase Ire1p is a site-specific endonuclease that initiates mRNA splicing in the unfolded protein response

Cell. 1997 Sep 19;90(6):1031-9. doi: 10.1016/s0092-8674(00)80369-4.


The endoplasmic reticulum (ER) communicates with the nucleus through the unfolded protein response (UPR), which senses accumulation of unfolded proteins in the ER lumen and leads to increased transcription of genes encoding ER-resident chaperones. As a key regulatory step in this signaling pathway, the mRNA encoding the UPR-specific transcription factor Hac1p becomes spliced by a unique mechanism that requires tRNA ligase but not the spliceosome. Splicing is initiated upon activation of Ire1p, a transmembrane kinase that lies in the ER and/or inner nuclear membrane. We show that Ire1p is a bifunctional enzyme: in addition to being a kinase, it is a site-specific endoribonuclease that cleaves HAC1 mRNA specifically at both splice junctions. The addition of purified tRNA ligase completes splicing; we therefore have reconstituted HAC1 mRNA splicing in vitro from purified components.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Basic-Leucine Zipper Transcription Factors
  • Endonucleases / genetics
  • Endonucleases / metabolism
  • Fungal Proteins / chemistry
  • Fungal Proteins / genetics*
  • Fungal Proteins / metabolism*
  • Membrane Glycoproteins / chemistry
  • Membrane Glycoproteins / genetics*
  • Membrane Glycoproteins / metabolism*
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Molecular Sequence Data
  • Nucleic Acid Conformation
  • Protein Folding
  • Protein Kinases / chemistry
  • Protein Kinases / genetics
  • Protein Kinases / metabolism
  • Protein Serine-Threonine Kinases*
  • RNA Ligase (ATP) / metabolism
  • RNA Splicing / physiology*
  • RNA, Messenger / chemistry
  • RNA, Messenger / metabolism*
  • Repressor Proteins / genetics
  • Saccharomyces cerevisiae / enzymology
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae Proteins*
  • Sequence Homology, Amino Acid
  • Substrate Specificity
  • Transcription Factors*


  • Basic-Leucine Zipper Transcription Factors
  • Fungal Proteins
  • HAC1 protein, S cerevisiae
  • Membrane Glycoproteins
  • Membrane Proteins
  • RNA, Messenger
  • Repressor Proteins
  • Saccharomyces cerevisiae Proteins
  • Transcription Factors
  • Protein Kinases
  • IRE1 protein, S cerevisiae
  • Protein Serine-Threonine Kinases
  • Endonucleases
  • RNA Ligase (ATP)