Abstract
Viable deletion mutants of actinophage R4 have been isolated using a pyrophosphate treatment. One of the deletion mutants, named R4Δ2, was shown to have a deletion of 0.98 megadaltons. A successful cloning of foreign DNA previously cleaved by SmaI endonuclease demonstrated that a unique PvuII site of R4Δ2 DNA was located in a dispensable region. The usefulness of R4 deletion mutants as cloning vectors in Streptomycesis discussed.
