A new class of genetically transmitted retravirus isolated from Mus cervicolor.

The cocultivation of spleen cells from the Southeast Asian mouse, Mus cervicolor, with heterologous cell lines has permitted the isolation of a new retravirus (designated M432) that can be transmitted to tissue culture cells of the laboratory mouse, M. musculus. Cells infected with M432 contain cytoplasmic type A particles and budding forms with compact,spherical nucleoids; extracellular virions lack surface spikes and have a condensed, central core surrounded by an intermediate line. Like other retraviruses, M432 bands isopycnically in sucrose at 1.16-1.17 g/cm3 and contains a 70S RNA genome composed of 35S subunits and an RNA-dependent DNA polymerase (RNA-dependent DNA nucleotidyltransferase). The viral reverse transcriptase requires magnesium as a cofactor and transcribes the synthetic template:primer poly(rC)-oligo(dG) more efficiently than poly(rA)-oligo(dT). [3H]DNA transcripts of the viral RNA genome detect multiple copies of endogenous virogene sequences in the cellular DNA of normal M. cervicolor, and fewer copies in heterologous cells infected with M432. Partially related nucleic acid sequences are also detected in the DNA of M. caroli and M. musculus as well as in more distantly related species (rat and hamster), reflecting the evolutionary conservation of these gene sequences in rodents. Although the virus from M. cervicolor shares certain morphologic and biochemical properties with murine type B viruses, the new isolate is unrelated by nucleic acid hybridization criteria to the mouse mammary tumor virus, the bovine leukemia virus, the Mason-Pfizer monkey virus, or known murine type C viruses, including endogenous type C viruses isolated from M. cervicolor.