Endoplasmic reticulum (ER) membrane-resident kinase/endoribonuclease involved in unfolded protein response (UPR) (PubMed:23066505). Initiates the selective decay of a subset of ER-localized-mRNAs that is required to survive ER stress (PubMed:23066505). Rather than relying on a transcriptional program to up-regulate genes that enhance ER protein folding capacity as in S.cerevisiae, S.pombe cells reduce the amount of specific proteins entering the organelle by decreasing the level of ER-targeted mRNAs using ire1-dependent mRNA degradation (PubMed:23066505). The sole mRNA cleaved upon ire1 activation that escapes decay is the ER chaperone bip1 mRNA which is more stable and hence is present at an increased steady-state after ire1 cleavage (PubMed:23066505). Promotes ER stress-induced ER-phagy and via up-regulation of the protein level of the ER-phagy receptor epr1 (Ref.5). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Impairs ER stress-induced ER-phagy. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.