The eps15 (EGF receptor pathway substrate clone number 15) gene was isolated using an expression cloning method designed for direct isolation of cDNAs encoding substrates of tyrosine kinases. The eps15 gene encodes a 145 kDa protein that is tyrosine phosphorylated following EGF receptor activation and this receptor directly phosphorylates purified Eps15 in vitro. Phosphorylation of Eps15 is much more efficient following EGF receptor activation versus erbB2 kinase activation, suggesting the protein is predominantly a part of an EGF receptor signaling pathway. Overexpression of Eps15 causes transformation of NIH 3T3 cells, implying Eps15 may be involved in the control of cell proliferation. Eps15 binds to the SH3 domain of Crk through its proline-rich domain at the C-terminal region. Adaptin α binds to the C-terminus of Eps15 at three different sites ranging from residues 650 to 730. Eps15, Adaptin α, and EGF receptor are co-localized at the clathrin-coated pits after receptor activation. Therefore, Eps15 may recruit EGF receptors to the clathrin-coated pits for internalization of the activated receptor.