Genetic instability associated with insertion of IS6100 into one end of the Streptomyces lividans chromosome.

Analysis of 548 recombinant strains of Streptomyces lividans carrying chromosomal insertions of IS6100 revealed that six mutants contained DNA amplifications. The amplifications differed in size but included IS6100 sequences. Hybridization with representative cosmid clones containing sequences from the unstable regions of the chromosome indicated that, in each mutant, DNA rearrangements affected just one of the chromosome ends. The amplifications were derived either from a region immediately proximal to the terminal inverted repeat (TIR) or further distal, from a previously characterized type I amplifiable unit of DNA. There was no evidence for extensive deletions accompanying the amplifications and chromosome linearity was maintained with, at least in five mutants, clear evidence for no loss of either TIR. The nature of the rearrangements provides evidence that insertions affecting the integrity of a chromosome end can contribute to genetic instability in Streptomyces.