Segregation of genetic information for a B-tropic leukemia virus with the structural locus for BALB:virus-1

A B-tropic type-C RNA virus isolatable from lymphoreticular tumors of the inbred BALB/c mouse strain has previously been shown to be leukemogenic in its natural host. This virus is not chemically inducible from BALB/c embryo cells or from embryo lines containing segregating inducibility loci for two known endogenous type-C viruses of BALB/c cells. Molecular hybridization and type-specific immunologic assays demonstrate a high degree of genetic homology between the B-tropic leukemia virus and BALB:virus-1, an N-tropic endogenous virus of BALB/c cells. Genetic sequences specific for BALB:virus-1 are shown to segregate with the locus for BALB:virus-1 induction in genetic crosses between BALB/c and the noninducible NIH Swiss strain. Thus, if the information of the B-tropic virus is encoded in the genome of the animal, it must be closely linked to the structural locus for BALB:virus-1. The evidence is consistent with a mechanism by which a small genetic alteration in BALB:virus-1 leads to a virus, whose growth is unrestricted, and subsequently to the development of neoplasia.