Different serotypes of B-tropic murine leukemia viruses and association with endogenous ecotropic viral loci

Abstract

We have previously presented evidence suggesting that the B-tropic viruses isolated from C57BL mice are generated through recombination of the endogenous N-tropic virus with an endogenous xenotropic virus. To further study the origin of B-tropic viruses and to genetically map the determinants of N/B-tropism, we have isolated 22 new N- and 13-tropic viruses from several strains of mice and have characterized their gene products serologically. For comparison, we have characterized an additional 14 N- and B-tropic viruses obtained from other sources. All of the N-tropic viruses had AKR-like p12s and p30s which competed in a radioimmunoassay specific for endogenous N-tropic p30s. Eight of nine 13-tropic viruses from three different substrains of C57BL mice had xenotropic-type p12s demonstrating that recombination involved the gag gene region. In contrast, 8 of 8 B-tropic viruses from BALB/c mice were characterized by AKR-like p12s. All 23 of the B-tropic viruses in the study have p30s that fail to compete in the specific p30 assay. These results demonstrate that there is strain specificity in the type of recombination resulting in generation of B-tropic viruses, although in both cases the p30 region is involved. The influence of the endogenous N-tropic viral locus on the type of B-tropic viruses is indicated by the observation that 3 of 4 13-tropic viruses isolated from C57BL/6 mice carrying the C3H ecotropic viral locus resembled the BALB/c 13-tropics, rather than the C57BL B-tropic viruses.