A specific probe for detecting ecotropic murine leukemia virus sequences was constructed by cloning a 400 base-pair DNA, corresponding to a portion of the env region of the AKR ecotropic virus. We have employed this probe to detect the presence or absence of ecotropic retroviral DNA sequences in 12 inbred strains of mice using the Southern blotting hybridization procedure. Our results show that between 2 and 6, and 1–2 copies of the ecotropic viral genome are present in mice with high or low incidence of leukemia, respectively. Ecotropic viral sequences are either absent or present in partial copies in mouse strains which heretofore failed to yield ecotropic viruses.
Present address: Institute of Organic Chemistry, Syntex Research, Palo Alto, California 94304.