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We have cloned and sequenced a complementary DNA encoding the cellular homologue of the transforming oncogene v-crk of avian sarcoma virus CT10. This complementary DNA contains an open reading frame of 915 base pairs that encodes a polypeptide of 305 amino acids. The first 205 amino acids of this c-Crk protein were identical to those of the CT10 encoded v-Crk protein, with the exception of 5 amino acids. Like v-Crk, this portion of c-Crk contained one each of the Src homology domains SH2, SH2', and SH3. The 100 carboxy-terminal amino acids of c-Crk protein, which are not coded for in the CT10 viral genome, contain another SH3 region. We found limited sequence homology between c-crk and the avian retrovirus genome, which explains recombination events in the transduction of this protooncogene. Using a polyclonal antiserum made against bacterially expressed v-crk, we identified a 35-kilodalton protein in normal chicken embryo fibroblasts and in all embryonic chicken tissues examined. This 35-kilodalton protein was indistinguishable from a polypeptide made by in vitro translation of c-crk complementary DNA. |
