p185, a product of the neu proto-oncogene, is a receptorlike protein associated with tyrosine kinase activity.

The neu oncogene was originally identified in cell lines derived from rat neuroectodermal tumors. neu is related to but distinct from the c-erbB gene, which encodes the epidermal growth factor (EGF) receptor. neu encodes a protein, designated p185, that is serologically related to the EGF receptor. Identification of the normal homolog of p185 encoded by the neu proto-oncogene enabled us to compare the product of the neu proto-oncogene with the mutated version specified by the neu oncogene and with the EGF receptor. The normal form of p185 was structurally similar to its transforming counterpart, indicating that activation of the neu oncogene did not cause major structural alterations in the gene product. Both normal and transforming forms of p185 were associated with tyrosine kinase activity, supporting the idea that normal p185 functions as a growth factor receptor. p185 differed both structurally and functionally from the EGF receptor. p185 and the EGF receptor had distinct electrophoretic mobilities when synthesized under normal culture conditions or in the presence of tunicamycin. EGF did not stimulate increased turnover of p185 and did not bind quantitatively to p185. A number of other growth factors failed to stimulate degradation of p185 or tyrosine phosphorylation of p185 and are therefore unlikely to be ligands for p185.