The high leukemogenic potential of Gross passage A murine leukemia virus maps in the region of the genome corresponding to the long terminal repeat and to the 3' end of env.

The Gross passage A murine leukemia virus (MuLV) is a highly leukemogenic, ecotropic fibrotropic retrovirus. Its genome is similar to that of other nonleukemogenic ecotropic fibrotropic MuLVs but differs at the 3' end and in the long terminal repeat. To determine whether these modifications were related to its leukemogenic potential, we constructed a viral DNA recombinant in vitro with cloned infectious DNA from this highly leukemogenic Gross passage A MuLV and from a weakly leukemogenic endogenous BALB/c B-tropic MuLV. Infectious viruses, recovered after microinjection of murine cells with recombinant DNA, were injected into newborn mice. We show here that the Gross passage A 1.35-kilobase-pair KpnI fragment (harboring part of gp70, all of p15E, and the long terminal repeat) is sufficient to confer a high leukemogenic potential to this recombinant.