The Fos Family: Gene and Protein Structure, Homologies, and Differences
The c-fos proto-oncogene was first isolated as the cellular homologue of two viral fos oncogenes encoded by the Finkel-Biskis-Jenkins and Finkel-Biskis-Reilly murine sarcoma viruses both of which induce osteosarcomas in rats and mice. The c-fos gene is 4 kbp long, including the proximal promoter sequences, and is interrupted by three introns. The fosB gene is similar to c-fos in both its genomic structure and with respect to the coding part. Several domains have been localized within the Fos protein that serve both common as well as separate molecular functions. The most important of these domains is a region in the central part of the protein that is indispensable for TRE-dependent transcriptional activation and morphological transformation, two properties of Fos that seem to be closely linked. Apart from confirming structural predictions of the Fos/Jun protein interactions, leucine zipper mutants have been valuable in dissecting the molecular mechanisms through which Fos and Jun exert their transregulatory function.