A type-I transmembrane protein complex located in the endoplasmic reticulum (ER) consisting of an IRE1-IRE1 dimer, which forms in response to the accumulation of unfolded protein in the ER. The dimeric complex has endoribonuclease (RNase) activity and evokes the unfolded protein response (UPR) by cleaving an intron of a mRNA coding for the transcription factor HAC1 in yeast or XBP1 in mammals; the complex cleaves a single phosphodiester bond in each of two RNA hairpins (with non-specific base paired stems and loops of consensus sequence CNCNNGN, where N is any base) to remove an intervening intron from the target transcript. [ http://www.ncbi.nlm.nih.gov/pubmed/18191223 http://www.ncbi.nlm.nih.gov/pubmed/25437541 ]