Transcriptional activator. Binds DNA as a dimer. The cleaved N-terminal cytoplasmic domain translocates into the nucleus. Controlled by regulated intramembrane proteolysis (RIP). 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) (By similarity). Belongs to the bZIP family. ATF subfamily.