Function: Transcriptional activator that may play a role in the unfolded protein response. Binds to the UPR element (UPRE) but not to CRE element. Preferentially binds DNA with to the consensus sequence 5'-T[GT]ACGT[GA][GT]-3' and has transcriptional activation activity from UPRE. Binds to NF-kappa-B site and has transcriptional activation activity from NF-kappa-B-containing regulatory elements. Tissue specificity: According to PubMed:11830526, exclusively expressed in the prostate. Expressed in breast and prostate cancer cell lines. Expressed in prostatic luminal epithelial cells (at protein level). Expression is significantly more abundant in prostate cancer than in benign prostatic tissue (prostatic hyperplasia). According to PubMed:12111373, also expressed in brain, pancreas and skeletal muscle, and at lower levels in small intestine, testis, leukocyte and thymus. Similarity: Belongs to the bZIP family. ATF subfamily. Contains 1 bZIP domain. PTM: N-glycosylated in the C-terminal region. Controlled by regulated intramembrane proteolysis (RIP). Following ER stress a fragment containing the cytoplasmic transcription factor domain is released by proteolysis. The cleavage seems to be performed sequentially by site-1 and site-2 proteases (PS1 and PS2). PS1 cleavage may be suppressed by a determinant in the C-terminal region.