A type-I transmembrane protein complex located in the endoplasmic reticulum which forms in response to the accumulation of unfolded protein in the ER and evokes the unfolded protein response (UPR) by splicing the mRNA encoding master transcriptional regulators of the UPR, Hac. It 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. Its catalytic activity depends on its conformation as a dimer and oligomer. (Gene Ontology, GO_1990332)
