Association of specific DNA binding and transcriptional repression with the transforming and myogenic activities of c-Ski

The ski oncogene encodes a transcription factor that induces both transform ation and muscle differentiation in avian fibroblasts. The first 304 amino acids of chicken Ski, the transformation domain, are both necessary and suf ficient to mediate these biological activities. Ski's biological duality is mirrored by its transcriptional activities: it coactivates or corepresses transcription depending on its interactions with other transcription factor s. Ski represses transcription through specific binding to GTCTAGAC (GTCT e lement) but it possesses a transferable repression activity that can functi on independently of this DNA element. In this study, we locate this repress ion domain to the NH2-terminal two-thirds and the GTCT binding region to th e COOH-terminal one-third of Ski's transformation domain. Mutations in the transformation domain of c-Ski reveal a strong correlation between GTCT-med iated transcriptional repression and the biological activities of transform ation and myogenesis. We also show that a dimerization domain located at th e COOH terminal end of the Ski protein increases its transforming activity and its binding to GTCTAGAC.