Rabbit Anti-Human IRE1? polyclonal antibody for IP, IF, WB. The gene ERN1 (endoplasmic reticulum to nucleus signaling 1) encodes an ER transmembrane kinase/endoribonuclease that is also referred to as IRE1? (inositol-requiring transmembrane kinase and endonuclease 1?). The serine-threonine protein kinase encoded by this gene is ubiquitously expressed in cells and tissues. It serves as an ER stress sensor that initiates the splicing of the mRNA encoding X-box–binding protein 1 (XBP-1) upon activation. Spliced XBP-1 mRNA produces homeostatic transcription factor XBP1. Under ER stress, the RNase activity of IRE1? cleaves many ER-localized mRNAs associated with apoptosis. The cytosolic motif of the activated form of IRE1? associates with the adaptor protein TRAF2 (tumor necrosis factor (TNF)–associated factor 2). This complex activates the c-Jun N-terminal kinase (JNK) signaling pathway.