Cellular Proteins Homologous to the Viral Yes Gene Product

We raised antibodies in rabbits against the amino-terminal portion of the viral yes protein produced in bacteria with the use of an expression vector based on the lac operon. The anti-yes serum thus obtained precipitated P90gag-yes from Yamaguchi 73 virus-transformed chicken embryo fibroblasts, and this immunoprecipitation was blocked by the purified antigen. The anti-yes serum did not recognize viral src, fps, or fgr proteins. Affinity-purified anti-yes immunoglobulin G (IgG) precipitated two proteins of 59 and 62 kilodaltons from lysates of normal chicken embryo fibroblasts. Two-dimensional tryptic peptide mapping showed that these proteins are closely related to P90gag-yes and that they are different from pp60c-src. Similar to P90gag-yes, the 59- and 62-kilodalton proteins were phosphorylated exclusively on tyrosine in an in vitro kinase reaction, whereas in vivo they were phosphorylated on serine and, to a lesser extent, on tyrosine as well. Expression of the 59- and 62-kilodalton proteins, determined by the immune complex kinase assay, was relatively high in brain, retina, kidney, and liver. The presence in normal chicken embryo fibroblasts and in chicken kidney of two transcripts, 3.7 and 3.9 kilobases in length, that hybridize with a yes-specific DNA probe, as well as the two proteins recognized by anti-yes IgG, suggests either differential splicing of cellular yes gene transcripts or the existence of another yes-related gene.