Structure of endogenous murine leukemia virus DNA in mouse genomes

By using molecularly cloned ecotropic AKR murine leukemia virus (MuLV) DNA, a 400-base-pair ecotropic type-specific segment in the env region has been identified. This DNA segment and other defined viral subgenomic fragments have been used as 32P-labeled probes to identify and analyze the structure of integrated ecotropic viral DNA sequences in uninfected mouse genomes. Those mice from which endogenous ecotropic MuLV of the AKR type have been isolated contained at least one virtually complete linear copy of the viral genome. Strains from which ecotropic MuLV has not been isolated lacked ecotropic-specific sequences. All inbred mouse strains tested also contained MuLV DNAs of genomic length whose restriction endonuclease digestion pattern was characteristic of xenotropic viruses.