A general approach to construct double deletion mutants of SV40

A procedure is described for the construction of double deletion mutants of SV40 from two parental viruses, each carrying a deletion sequence at a specific region. The construction steps involve heteroduplex formation between two parental DNA molecules, nuclease Sl treatment, and subsequent cloning of the duplexes after infection in the permissive cell. Two such mutants were obtained: One contains both deletions in the late gene region; and the other contains one deletion in the early region and another in the late region. These mutants were derived from their respective deletion mutants as shown by restriction enzyme analysis of their DNA genomes.