Molecular cloning of integrated simian sarcoma virus: genome organization of infectious DNA clones.

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Abstract
The integrated form of simian sarcoma virus (SSV) was molecularly cloned in the Charon 16A strain of bacteriophage .lambda.. In transfection analysis, the recombinant viral DNA demonstrated the ability to transform cells [mouse fibrobast 3T3 cells and normal rat kidney NRK cells] in tissue culture at high efficiency. Such transformants possessed typical SSV morphology, expressed simian sarcoma associated virus (SSAV) gag gene products in the absence of virus release, and released SSV after superinfection with a type C helper virus. A physical map of the 5.8-kilobase-pair (kpb) recombinant viral DNA clone, deduced from restriction endonuclease analysis, revealed a 5.1-kbp SSV genome containing 0.55-kbp-long terminal repeates flanked by 0.45 and 0.25 kbp of contiguous host cell sequences. By R-loop analysis, the viral DNA molecule contained 2 regions of homology to SSAV, separated by a 1.0-kbp nonhomologous region. This SSV-specific sequence was uniquely represented within the normal cellular DNA of diverse mammalian species, including human. This primate transforming retrovirus apparently arose in nature by recombination of a type C helper virus and a host cellular gene.