GENETIC INSTABILITY OF THE STREPTOMYCES CHROMOSOME

The Streptomyces wild-type chromosome is linear in all examples studie d. The ends of the chromosome or telomeres consist of terminal inverte d repeats of various sizes with proteins covalently bound to their 5' ends. The chromosome is very unstable and undergoes very large deletio ns spontaneously at rates higher than 0.1% of spores. Frequently, the telomeres are included in the deletions. Loss of both telomeres leads to circularization of the chromosome. The wildtype chromosome can also be circularized artificially by targeted recombination. Spontaneously or artificially circularized chromosomes are even more unstable than the linear ones. High-copy-number tandem amplifications of specific ch romosomal regions are frequently associated with the deletions. RecA s eems to be involved in the amplification mechanism and control of gene tic instability.