Lin Y-S, Chen C. W. (1997)

Instability of artificially circularised chromosomes of Streptomyces lividans.

Molecular Microbiology, 26: 709-719.

ABSTRACT

The chromosomes of Streptomyces species are linear molecules, containing long terminal inverted repeats and covalently bound terminal proteins. These chromosomes undergo spontaneous deletions of the terminal sequences at high frequencies, and become circularised in several cases examined. Artificial circularisation of the Streptomyces lividans chromosome was also achieved by targeted recombination in vivo, in which the terminal inverted repeats of the chromosome were connected by a kanamycin resistance gene (aphII). Under kanamycin selection, the circularised chromosomes harboured tandem amplifications of a 20.2-kb sequence that included the aphII gene flanked by direct repeats, and deletions near by. On release from kanamycin selection, the aphII amplifications and the neighbouring sequences were deleted from the chromosomes, rendering all the cultures kanamycin sensitive. The chloramphenicol resistance gene, which was prone to deletion in wild type S. lividans, became much more stable in the kanamycin sensitive derivatives. These results indicate that the telomeres and/or certain terminal sequences may be involved in the structural instability of Streptomyces chromosomes.