In vitro mutagenesis of the v-sis transforming gene defines functional domains of its growth factor-related product.

The polypeptide sequence of the v-sis transforming gene product of simian sarcoma virus (SSV) can be divided into four regions that are likely to represent structural domains of the protein. Mutations were generated in the SSV nucleotide sequence to assay the extent or function of each of these regions. The results indicate that the helper virus-derived amino-terminal sequence as well as a core region homologous to polypeptide chain 2 of platelet-derived growth factor (PDGF) are required for the transforming function of the protein. Products of transforming but not nontransforming mutants formed dimer structures conformationally analogous to biologically active PDGF.