Isolation and characterization of covalently closed circular DNA associated with chromosomal and membrane fraction from Streptomyces ambofaciens.

Covalently closed circular (ccc) DNAs were isolated by a technique involving alkaline denaturation from the spiramycin producer Streptomyces ambofaciens KA-1028 and also from spiramycin non-producing strains AF-11 and QN-25; plasmids could not be detected in these strains by a cleared lysate method. It was found that most of the ccc DNA in these strains was present in the chromosomal and membrane fractions. These ccc DNAs had identical mobilities in agarose gel electrophoresis. The size was calculated to be 53.1 x 10(6) daltons from the contour length measurements. The ccc DNA gave one fragment on digestion with Hind III, three fragments with Eco R1, and twenty-eight fragments with Bam H1.