Component of the AP-1 transcription factor that represses transactivation mediated by the Jun family of proteins. Involved in a variety of transcriptional responses associated with AP-1 such as UV-induced apoptosis, cell differentiation, tumorigenesis and antitumogeneris. Can also function as a repressor by recruiting histone deacetylase 3/HDAC3 to the promoter region of JUN. May control transcription via direct regulation of the modification of histones and the assembly of chromatin. Forms a homodimer or heterodimer with JUN, JUNB, JUND, CEBPG and ATF2 thereby inhibiting transactivation by JUN, ATF2 and CEBPG (By similarity). Binds multiple DNA elements such as cAMP-response element (CRE) and TPA response element (TRE) either as homodimer or heterodimer (By similarity). Interacts with IRF2BP1. Phosphorylation of Thr-148 by MAPK8 in response to different stress conditions such as, UV irradiation, oxidatives stress and anisomycin treatments. Polyubiquitinated; probably by IRF2BP1. Belongs to the bZIP family. ATF subfamily.