Squirrel monkey retrovirus: an endogenous virus of a new world primate.

Squirrel monkey retrovirus (SMRV) was isolated by cocultivation of squirrel monkey lung cells with canine cells. 3H-labeled 60-70S SMRV RNA, isolated from virus grown in canine cells, hybridized to the same extent and to the same Cot1/2 value to the DNA of all tissues of all squirrel monkeys tested; Cot1/2 values show that SMRV proviral sequences are present in the low repetitive range. No SMRV proviral sequences were detected in tissues from a variety of other New World monkeys, Old World monkeys, or apes. Murine, feline, bovine, and canine cells also contain no detectable SMRV proviral sequences. Competitive molecular hybridization studies revealed no detectable sequence homology between the 60-70S RNAs of SMRV and Mason-Pfizer virus (MPV). The virion-associated DNA polymerase of SMRV is similar to that of MPV in that it has a molecular weight of approximately 80,000 and prefers magnesium as a divalent cation using oligo(dG)-poly(rC) as primer-template. The virion-associated DNA polymerase of SMRV can be clearly distinguished from those of MPV and the mouse mammary tumor viruses, however, by its preference for manganese as a divalent cation in the presence of high salt.