The MyoD cDNA, when expressed under the control of a viral LTR and transfected into a variety of fibroblast and adipoblast cell lines, converts these cells to muscle. While not yet proven MyoD acts as if it were a master regulatory gene for myogenesis. The MyoD protein is nuclear and preliminary work suggests it binds DNA. The present proposal is to: (1) Characterize MyoD using detailed mutagenic analysis. (2) Study its binding to specific DNA sequences; study its interaction with other cellular proteins. (3) Explore preliminary indications that MyoD positively activates its own synthesis but negatively activates its mRNA utilization.