Transcription factor involved in endoplasmic reticulum (ER) stress response (PubMed:21223397, PubMed:22050533, PubMed:22199238). Acts downstream of the ER stress sensors IRE1, BZIP39 and BZIP60 to activate BiP chaperone genes (PubMed:22050533, PubMed:22199238). Transcriptionally activated by IRE1 in response to endoplasmic reticulum (ER) stress. IRE1 cleaves a 20-bp fragment causing a frameshift of the mRNA transcript, leading to a nuclear isoform of the BZIP50 activator. The bZIP domain is translocated into the nucleus in response to ER stress. By dithiothreitol-induced endoplasmic reticulum (ER) stress response (PubMed:22050533, PubMed:21223397). Induced by salt stress (PubMed:22050533). Potent transcriptional activator. Induced by IRE1 in response to endoplasmic reticulum stress. IRE1 cleaves a 20-bp fragment causing a frameshift of the mRNA transcript. Belongs to the bZIP family.