Polypeptides of Mason-Pfizer monkey virus. III. translational order of proteins on the gag and env gene specified precursor polypeptides

Mason-Pfizer monkey virus (M-PMV), the prototype D-type retrovirus, unlike most retroviruses, preassembles core structures in the cytoplasm of infected cells during morphogenesis. We have shown previously ( J. Bradac and E. Hunter, 1984 , Virology 138, 260–275) that M-PMV virions contain 5 gag-encoded polypeptides. In this report, the translational order of the proteins encoded on the gag and env genes of M-PMV has been determined by pactamycin mapping. The proposed order of the viral proteins on their respective precursors is env: NH2-gp85-gp20-COOH; gag: NH2-p10-pp24/pp16-p12-p27-p14000H. Myristic acid-labeled virions contained a single radioactive protein, p10, supporting the mapping of this molecule to the amino terminus. From these studies it is clear that M-PMV contains an unusual additional gag polypeptide, p12, for which no function has been assigned to date. A remarkable similarity exists in the size and organization of M-PMV and mouse mammary tumor virus (MMTV) gag polypeptides; suggesting a common ancestor to these two viruses.