Reverse transcriptase in normal rhesus monkey placenta.

Particles with the morphology of type C virus have been identified from primate placentas by electron microscopy. A reverse transcriptase (RNA-dependent DNA polymerase) was isolated and purified from microsomal pellets of two fresh placentas of rhesus monkeys in the early stages of gestation. This enzyme was biochemically similar yet immunologically distinct from the reverse transcriptases of known tumorigenic type C RNA viruses isolated from primates, but was immunologically related to a reverse transcriptase isolated from a type C virus obtained from normal baboon placenta. These particles may represent endogenous viruses and may function in the transfer of genetic information during embryogenesis.