Characterization of the human c-myc protein using antibodies prepared against synthetic peptides.

Synthetic peptides with amino acid sequences based on inferred sequences encoded by the human c-myc proto-oncogene have been used as immunogens to produce polyclonal and monoclonal antibodies. These peptide-specific antibodies have then been used to identify the intact human c-myc protein. By immunoprecipitation and immunoblotting analysis we have defined the human c-myc protein as a phosphoprotein with an apparent molecular mass of 62 kDa on a sodium dodecyl sulphate-polyacrylamide gel. The protein is present in both normal and transformed cells but the steady-state levels of p62c-myc are elevated in the transformed cells by comparison with normal ones. We have used our anti-c-myc peptide antibodies to study the subcellular localization of p62c-myc. We find the protein to be loosely associated with cell nuclei by an interaction which is highly sensitive to variations in ionic strength within the physiological range. In response to in vitro or in vivo heat-shock the protein becomes sequestered in an insoluble complex associated with the nucleus. This complex contains a discrete subset of nuclear proteins, of which p62c-myc is a member. Immunofluorescence microscopy of p62c-myc shows it to be localized in a defined and previously unobserved subnuclear structure. A role for p62c-myc as an intracellular messenger is suggested.