Highly transformable mutants of Streptomyces aureofaciens containing restriction-modification systems.

Streptomyces aureofaciens 13 is a mutant defective in chlortetracycline production. It was chosen as a potentially useful host for gene cloning in investigations of the organization of the biosynthetic genes for the tetracycline antibiotic pathway. From the Streptomyces aureofaciens 13 strain, three suitable clones were used for our work. The conditions for optimal formation and efficient transformation of protoplasts with plasmid DNAs have been determined. Transformation frequencies of about 10(4) to 10(5) per microgram of plasmid DNA were obtained when plasmids were isolated from Streptomyces strains. From the patterns of restriction enzyme digestion of plasmid DNA isolated from Streptomyces aureofaciens transformants, it was observed that the clones express modification systems which render plasmid DNAs resistant to cleavage by HindIII and EcoRI. Additionally, one of the clones produces the restriction endonuclease Sau13I (isoschizomer of SauI). The presence of the restriction-modification system of Sau13I does not reduce the efficiency of plasmid transformation.