An endogenous oncornavirus of guinea pigs: its expression in leukemic cells

Guinea pigs do not have any known infectious oncornaviruses. We have recently activated an endogenous oncornavirus (GPV) from cultured guinea pig cells after bromodeoxyuridine riboside (BUdR) treatment. GPV is noninfectious for guinea pig cells and is inducible from any guinea pig cell in culture. Although the morphogenesis of the activated virus is unique, it has the morphology and density (1.16 g/ml) of type C oncornaviruses. It contains an oncornavirus specific reverse transcriptase and a high molecular weight RNA (70S) which dissociates into 36S following denaturation. GPV contains 5 major protein components (mol. wt. 95,000 to 16,000 daltons), 2 of which are glycoproteins. The viral genome which remains repressed in normal cells is expressed in leukemic guinea pig cells. These leukemic cells contain particles which have the morphological and biochemical characteristics of BUdR activated endogenous viruses. Unlike the cells transformed by infectious oncornaviruses, the leukemic cells contain the same amount of virus specific DNA present in normal cells.