Characterization of a family of multimeric ccc molecules of amplified chromosomal DNA in Streptomyces ambofaciens DSM 40697

A spontaneous mutant strain of Streptomyces ambofaciens DSM 40697, a producer of spiramycin, defective in pigment and aerial mycelium formation was isolated. The DNA analysis revealed the presence of an amplified DNA sequence (ADS). This ADS was characterized, localized on the chromosome within the AUD6 region and a rearrangement on one side of the ADS was detected. Experiments led to the detection and characterization of an extrachromosomal multimeric ccc (covalently closed and circular) DNA molecule family. The monomeric form presented a size similar to the previous ADS and all multimeric forms were homologous with it.