has role AP-1 The AP-1 (activator protein 1) transcription factor is a dimeric complex that comprises members of the JUN, FOS, ATF (activating transcription factor) and MAF (musculoaponeurotic fibrosarcoma) protein families. The AP-1 complex can therefore form many different combinations of heterodimers and homodimers, and this combination determines the genes that are regulated by AP-1. transcription regulator molecular complex