The Activator protein 1 (AP1) transcription factor is a dimeric transcription factor whose subunits belong to four different families of DNA-binding proteins including the Jun family, Fos family, ATF/cyclic AMP-responsive element-binding (CREB), and the musculoaponeurotic fibrosarcoma (Maf) family [54]. The gene discussed is JUN; the disease is fibrosarcoma.