A 66-kDa protein associated with epidermal growth factor receptor is a proteolytic fragment of phosphoinositide-specific phospholipase C.

It is shown that in the A431 cells, EGFR is co-immunoprecipitated with a group of proteins recognized by antibodies to phospholipase C gamma. These are 145- and 47-kDa proteins corresponding to phospholipase C gamma and Nck, respectively, and an unidentified 66-kDa protein. The association of phosphoinositide-specific phospholipase C gamma and 66-kDa protein to EGFR was observed in the A431 cells with or without the EGF treatment. Trypsin peptide maps of these two proteins are similar so it is assumed that the 66-kDa protein is related to phospholipase C gamma.