A simple method for immunoaffinity purification of nondenatured avian sarcoma and leukemia virus gag-containing proteins.

We have developed a one-step purification procedure for proteins containing the N-terminal portion of the gag protein of avian sarcoma and leukemia viruses. In this procedure, a resin with a covalently attached monoclonal antibody to the gag protein p19 is used to bind gag-containing proteins from crude extracts. After washing of the resin, the bound proteins are eluted with 2 M MgCl2. For the transforming protein kinase encoded by Fujinami sarcoma virus p130gag-fps, this procedure gave an enrichment of several thousand-fold, a yield of over 10%, a final purity of over 20%, and no significant loss of protein kinase activity. Similar purifications were obtained with three other gag-containing proteins. The immunoaffinity purification described may be of general utility as a first step in purification of the several other avian retroviral transforming proteins that are synthesized from fusions of an oncogene with the viral gag gene.