Gene order of the mouse mammary tumor virus glycoproteins

Immunochemical and tryptic peptide mapping techniques were used to show that the mouse mammary tumor virus (MMTV) envelope glycoproteins gp52 and gp36 are distinct components derived from a common glycosylated precursor polypeptide of 75,000 daltons (gPr75). Because both gp52 and gp36 are derived from a common precursor polypeptide and therefore have a common initiation site, we have been able to determine their gene order within the viral genome. The gene order was deduced from three different types of experiments. The first approach measured the differential inhibition by NaCl hypertonic shock on initiation of gp52 and gp36 synthesis. The second approach measured the kinetics of appearance of various MMTV proteins following the synchronized reinitiation of polypeptide synthesis resulting from NaCl hypertonic shock. The third approach analyzed polypeptides released from polyribosomes after a series of variable-length short pulses with [3H]amino acids. Our results indicate that the gene order for gPr75 is H2N-gp52-gp36-COOH and 5'-gp52-gp36-3' within the MMTV genome.