Localization of the src gene product of the Harvey strain of MSV to plasma membrane of transformed cells by electron microscopic immunocytochemistry.

Using electron microscopic immunocytochemistry, we have investigated the intracellular location of the src protein (p21) in cells transformed by the Harvey strain of Murine Sarcoma Virus (Ha-MSV). Antibodies to p21 were derived from tumor-bearing rats inoculated with Ha-NRK cells. The distribution of p21 in intracellular sites in MDCK dog cells transformed by Ha-MSV was examined and quantified using a recently developed immunocytochemical technique. More than 95% of p21 was localized to the inner surface of the plasma membrane in these Ha-MSV-transformed cells; p21 was not exposed on the outside surface of the plasma membrane. A similar location was observed by immunofluorescence in other Ha-MSV-transformed cell lines, including cells derived from rat, mouse and mink. This finding, and the previous demonstration that p60src of avian sarcoma virus is concentrated on the inner surface of the plasma membrane, suggests that the plasma membrane is a major site of action for transforming proteins.