Molecular cloning of murine endogenous viral sequences and expression of a newly constructed recombinant murine leukemia virus DNA in transfected mink cells.

In the process of molecularly cloning unintegrated proviral DNA from NIH-3T3 mouse cells infected with Rauscher murine leukemia virus, we observed the occurrence of clones with inserts smaller than the expected Rauscher murine leukemia virus fragments. The insert of one of these clones, lambda.Xe-1, was characterized in more detail. It had a size of 3.5 kilobases. The restriction map was similar but not identical to that of the envelope regions of Moloney and Rauscher murine leukemia viruses. After ligation to previously cloned Moloney murine leukemia viral sequences and transfection of the ligated DNA into mink lung cells a nondefective xenotropic murine leukemia virus, XH-19, was isolated. Restriction mapping of proviral DNA isolated from mink lungs cells chronically infected with XH-19 showed the presence of Moloney murine leukemia virus-derived sequences coupled to xenotropic viral sequences.