The oncogene of the Rous sarcoma virus (q.v.). The human SRC gene lies at 20 q12-q13, while the Drosophila Src gene is on the third chromosome at 64B. Src genes encode proteins that function as protein tyrosine kinases and are characterized by SH2 and SH3 domains. These are important for intra- and intermolecular interactions that regulate both the catalytic activity of the molecules and their recruitment of substrates. SH2 domain is about 100 amino acids long, while SH3 domain is about 50 amino acids long and is rich in proline. Src PTCs regulate the actin cytoskeleton, and they play a role in the morphogenesis of ring canals (q.v.) during oogenesis. See actin, c-src, domain, v-src.