Abstract
All vertebrate cells have been shown to contain a gene, sarc, that has some homology with the transforming gene of Rous sarcoma virus, src. We have compared the polypeptide products of the sarc gene, p60(sarc), of human, mouse, and chicken cells with the polymorphic polypeptide product of the src gene, p60(src), of several strains of Rous sarcoma virus by two-dimensional peptide mapping. p60(sarc) from chicken cells was clearly related to every viral p60(src). Eleven of its 13 methionine-containing tryptic peptides were present in some viral p60(src). Conversely, the other two peptides were not present in any p60(src) we have examined so far. The 11 peptides from p60(sarc) of chickens that were shared with viral p60(src), however, were not all present in any single viral p60(src). These 11 peptides most closely resemble those in the p60(src)s of B77 virus and the Prague strain of Rous sarcoma virus. These data are consistent with the hypothesis that cellular sarc is the progenitor of viral src. The p60(sarc)s of human, mouse, and chicken cells were so similar in tryptic peptide composition that they were more closely related to each other than were some viral p60(src)s. The two mammalian p60(sarc)s differed from avian p60(sarc) most notably in that they lacked a peptide that chicken p60(sarc) shares with all the viral p60(src)s. The similarity of these maps suggests that the sequence of the p60(sarc) polypeptide has diverged very little during evolution. This may imply that p60(sarc) is an essential cellular component.