ATF-1 a transcription factor that is a member of the leucine zipper family. Forms a homodimer or heterodimer with c-Jun and stimulates CRE-dependent transcription. Binds the Tax-responsive element (TRE) of HTLV-I. Activated downstream of IL-1. c-Src and TRAF6 are mediators of IL-1-induced AP-1 activation.