title: The role of individual cysteine residues in the structure and function of the v-sis gene product.
abstract: The v-sis oncogene encodes a platelet-derived growth factor (PDGF)-related product whose transforming activity is mediated by its functional interaction with the PDGF receptor. PDGF, as well as processed forms of the v-sis gene product, is a disulfide-linked dimer with eight conserved cysteine residues in the minimum region necessary for biologic activity. Site-directed mutagenesis of the v-sis gene revealed that each conserved cysteine residue was required directly or indirectly for disulfide-linked dimer formation. However, substitution of serine for cysteine codons at any of four positions had no detrimental effect on transforming activity of the encoded v-sis protein. These results establish that interchain disulfide bonds are not essential in order for this protein to act as a functional ligand for the PDGF receptor. The remaining four substitutions of serine for cysteine each inactivated transforming function of the molecule. In each case this was associated with loss of a conformation shown to involve intramolecular disulfide bonds. These studies provide insight into the role of individual cysteine residues in determining the structure of the sis/PDGF molecule critical for biological activity.
mesh_terms: D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000032:analysis / Q000502:physiology*; D002472:Cell Transformation, Viral; D003429:Cross Reactions; D003545:Cysteine; D005814:Genes, Viral; D009154:Mutation; D009856:Oncogene Proteins, Viral / Q000032:analysis / Q000502:physiology*; D009857:Oncogenes; D010982:Platelet-Derived Growth Factor / Q000032:analysis / Q000502:physiology; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D011956:Receptors, Cell Surface / Q000378:metabolism; D017479:Receptors, Platelet-Derived Growth Factor; D012190:Retroviridae / Q000235:genetics*; D012842:Sarcoma Virus, Woolly Monkey / Q000235:genetics*; D012694:Serine; D014162:Transfection
chemical_list: D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D009856:Oncogene Proteins, Viral; D010982:Platelet-Derived Growth Factor; D011956:Receptors, Cell Surface; D012694:Serine; D017479:Receptors, Platelet-Derived Growth Factor; D003545:Cysteine