Characterization of RNase H activity associated with reverse transcriptase in simian foamy virus type 1

Spumavirinae or foamy viruses have been shown to have a characteristic RNA-dependent DNA polymerase activity. We demonstrate here the existence of an RNase H activity that copurifies with the 81-kilodalton monomeric polypeptide, which carries the RNA-dependent DNA polymerase activity of simian foamy virus type 1. RNase H degrades RNA hybrid substrates; however, it does not solubilize single-stranded RNAs. Inactivation assays with heat, high levels of bivalent cations, ethidium bromide, and sodium fluoride suggest that the RNase H catalytic site could be topologically independent from the DNA polymerase catalytic site.