The nucleic acid sequence homology between various murine, endogenous type-C viruses (three host range classes of BALB/c virus, the AT-124 virus, and the CCL 52 virus) and two laboratory strains of murine leukemia virus (Rauscher and Kirsten) was determined by DNA:RNA hybridization. The viral sequences exhibit varying degrees of partial homology. DNA:DNA hybridizations were performed between [3H]DNA probes prepared from Nand X-tropic BALB/c endogenous viruses and cellular DNAs from BALB/c, NIH

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... wiss, and AKR inbred mouse strains as well as from California feral mice and the Asian mouse subspecies Mus musculus molossinus and M. musculus castaneus. All of these strains of mice are shown to possess multiple (six to seven per haploid genome), partially related copies of type-C virogenes in their DNAs. Thermal melting profiles of the DNA:RNA and DNA:DNA hybrids suggest that the partial homology of the viral nucleic acid sequences is the result of base alterations throughout the viral genomes, rather than the'loss of discrete segments of viral sequences.