c-Fos is a member of the AP-1 transcription factor family under the Fos protein family umbrella, alongside Fra-1, Fra-2 and Fos-B. Also in the AP-1 transcription family are the Jun proteins, c-Jun, Jun-B and Jun-D. Each member of the AP-1 transcription family is a phosphonuclear protein composed of a carboxy-terminal leucine zipper domai