Generation of nondefective Rous sarcoma virus by asymmetric recombination between deletion mutants.

A replication-defective deletion mutant of Prague Rous sarcoma virus (RSV), which lacks functional gag, pol, and env genes, was crossed with a transformation-defective deletion mutant derived from Schmidt-Ruppin RSV. Transformation- and replication-competent viruses were generated in the cross. Characterization of one of these rescued viruses indicated that it was a nondefective recombinant containing the src gene of the replication-defective mutant plus the replicative genes of the transformation-defective virus. These results indicate that, contrary to previous reports, asymmetric recombination between RSV deletion mutants can result in the formation of nondefective RSV.