Structure of an amplifiable DNA sequence in Streptomyces lividans 66

Spontaneous chloramphenicol-sensitive mutants of Streptomyces lividans 66 had previously been shown to be very unstable and to yield arginine auxotrophic mutants at a frequency of 25% of spores; the Arg- mutants had amplified a particular 5.7 kb DNA sequence to over one hundred tandem copies per genome. In this paper we report the cloning of the amplifiable region from amplified and wild-type strains. This showed that the amplifiable fragment is already present as a duplication in wild type cells. Hybridisation experiments also demonstrated that in the amplified strains there was a deletion of neighbouring DNA sequences to one side of the amplifiable element; sequences to the other side remain intact.