Abstract
Cell lines of four mammalian species were each examined for the number of Moloney murine sarcoma virus (M-MSV) DNA copies in total cellular DNA after M-MSV transformation. Sarcoma-positive, leukemia-negative (S+L-) M-MSV-transformed cells were compared to M-MSV-transformed cells infected with a replicating leukemia virus. Both unfractionated M-MSV complementary DNA and complementary DNA representing the MSV-specific and the MSV-murine leukemia virus-common regions of the M-MSV genome were hybridized to total cellular DNA of various species. DNAs of mouse, cat, dog, and human S+L-cells contained from less than one to a few proviral M-MSV DNA copies per haploid genome. In contrast, helper virus-coinfected, M-MSV-producing cells of each species showed a 3- to 10-fold increase in M-MSV proviral DNA over that found in corresponding S+L- cells. MSV-specific and MSV-murine leukemia virus-common nucleotide sequences were each increased to a similar degree. A corresponding examination of cellular DNA of leukemia virus-infected normal or S+L- mammalian cells was performed to establish the resulting number of leukemia proviral DNA copies. The infection of normal or S+L- mammalian cells with several leukemia-type viruses that did not have nucleotide sequences closely related to the cell before infection resulted in the appearance of one to three corresponding leukemia proviral DNA copies.