Reversal of Fv-1 host range by in vitro restriction endonuclease fragment exchange between molecular clones of N-tropic and B-tropic murine leukemia virus genomes.

We molecularly cloned unintegrated viral DNA of the BALB/c endogenous N-tropic and B-tropic murine leukemia retroviruses and in vitro passaged N-tropic Gross (passage A) murine leukemia retroviruses. Recombinant genomes were constructed in vitro by exchanging homologous restriction enzyme fragments from N- or B-tropic parents and subsequent recloning. Infectious virus was recovered after transfection of these recombinant genomes into NIH-3T3 cells and cocultivation with the Fv-1 nonrestrictive SC-1 cells. XC plaque assays of recombinant virus progeny on Fv-ln and Fv-lb cells indicated that the Fv-l host range was determined by sequences located between the BamHI site in the p30 region of the gag gene (1.6 kilobase pairs from the left end of the map) and the HindIII site located in the pol gene (2.9 kilobase pairs from the left end of the map).

Autogenous immunity to endogenous RNA tumor virus. Identification of antibody reactivity to select viral antigens.

The viral antigenic determinants recognized in an autogenous immune response in mice against their endogenous C-type virus have been identified by SDS-polyacrylamide gel electrophoresis of immune precipitates between various sera and H(3)-labeled intact or disrupted AKR leukemia virus. Normal B6C3F(1) [(C57BL/6 x C3H/Anf)F(1)] serum reacts with viral envelope antigens having mol wt of approximately 68,000, 43,000, and 17,000. In addition, minor reactions with viral antigens having mol wts of approximately 19,000 and 15,000 are demonstrable. The 68,000 and 43,000 mol wt antigens can be labeled with [(3)H]glucosamine and may correspond to the major viral envelope antigens M(2) and M(1), respectively. The antigens recognized by autogenous immune sera do not differ with respect to age of the animal, nor are they significantly different in sera from various strains of mice (BALB/c, C57BL/6, and C3H/Anf). These results suggest that the age-asociated and strain variations in the autogenous immune response, as determined by radioimmune precipitation assays against intact virus, are due to quantitative and qualitative alterations of antibody levels against common antigens.