Evidence That the AKR Murine-Leukemia-Virus Genome Is Complete in DNA of the High-Virus AKR Mouse and Incomplete in the DNA of the "Virus-Negative" NIH Mouse (mouse leukemia virus/AKR and NIH mouse DNA and RNA/IdU activation/reassociation kinetics)

The AKR mouse has a high titer of rnurine leukemia virus early in life, and virus-negative cells de- rived from embryos of this mouse strain can be activated to yield murine leukemia virus by treatment with 5-iodo- deoxyuridine. In contrast to this high-virus strain, the NIH Swiss mouse has a low incidence of leukemia and no murine leukemia virus has been isolated from it (virus- negative). We have investigated this difference between AKR and NIH mice by examining the sequences specific for murine leukemia virus in nucleic acids of these mice. A single-stranded viral-DNA probe synthesized in vitro using murine-leukemia-virus from the AKR mouse con- tains at least 87% of the sequences present in the 70S viral RNA; most of these sequences are in proportions similar to their content in the 70S RNA. Using this probe in nucleic acid hybridization experiments, we have shown