Abstract
The nucleic acid sequences found in DNA and RNA from rat cells which are homologous to Kirsten sarcoma virus have been characterized. The homologous sequences are present in multiple copies per diploid rat cellular genome in a variety of different rat cellular dna's. In certain cells that constitutively express only low levels of sequences homologous to Kirsten sarcoma virus, bromodeoxyuridine treatment leads to the expression of high levels of these sequences in RNA. Supernatants from cell lines producing the sequences homologous to Kirsten sarcoma virus contain high levels of these sequences which are purified to the same degree as the previously known rat type C viral nucleic acid sequences by type C particles being released from such cells. The results indicate that the sequences in rat cells homologous to Kisten sarcoma virus have three characteristics of known mammalian type C viruses, and suggest that at least part of Kirsten sarcoma virus rat-derived sequences represent a distinct class of endogenous rat type C virus that has no detectable homology to the other known class of endogenous rat type C virus.