Alterations in the genomes of avian sarcoma viruses.

We describe 12 nonconditional mutants of avian sarcoma virus. Eleven were replication defective and one appeared to retain wild-type functions. Comparison of restriction endonuclease digests of viral DNA revealed that 8 of 11 replication defectives contained large deletions of viral information. A functionally wild-type variant contained an insertion of sequences between the env and src genes. The deletions appeared to be randomly distributed throughout the replicative genes: gag, pol, and env. In most, but not all, cases, the phenotype of the deletion mutants could be simply correlated with the location and extent of the deletions. In a few cases, the defects in expression appeared to be more extensive than would be expected from a single point or deletion mutation, suggesting that these mutants contained multiple mutations or a single mutation in a region affecting several viral functions