Identification of DNA fragments carrying ecotropic proviruses of AKR mice

The proviruses of the N-tropic, ecotropic virus (AKV) of AKR mice (Akv-1, Akv-2) have been studied by the Southern gel--filter transfer technique. These proviruses can be detected by cleavage of cell DNA by BamHI endonuclease, which yields characteristic subgenomic DNA fragments upon cleavage of this type of provirus. Proviruses integrated into different sites in the mouse genome can be resolved with EcoRI endonuclease, which does not cleave the AKV proviruses. Use of congenic and backcrossed mice and a radioactive DNA probe enriched for AKV sequences has allowed identification of the EcoRI fragments carrying the proviruses of the genetically defined Akv-1 and Akv-2 loci. Novel proviruses introduced by superinfection of cultured AKR cells with AKV and present in leukemic cells from AKR mice have also been identified. Comparison of substrains of AKR mice indicates some heterogeneity in their spectra of proviruses.