Abstract
The serological properties of the gag gene products p15 and p12 of N- and B-tropic viruses of C57BL mice have been examined. Although these viruses were serologically identical by competition assays for proteins gp71 and p30, they were readily distinguishable in competition assays for proteins p15 and p12. Two isolates of N-tropic viruses had p12s serologically indistinguishable from AKR murine leukemia virus p12, while two B-tropic isolates had distinctly different p12s. The latter p12s were serologically indistinguishable from the p12 purified from the B-tropic radiation leukemia virus (RadLV)/VL-3. Moreover, this p12 was indistinguishable from the p12 of the endogenous C57BL/Ka xenotropic virus. Similarly, the p15s of the B-tropic viruses were serologically distinct from the AKR murine leukemia virus type of p15, as was the p15 of one C57BL N-tropic virus, whilc another N-tropic isolate had a p15 identical to the AKR murine leukemia virus p15. These results are interprered to suggest that the endogenous N-tropic virus of C57BL mice undergoes recombination with the endogenous, xenotropic virus and that this mechanism is involved in the generation of B-tropic viruses in C57BL mice.