DNA AMPLIFICATIONS AND DELETIONS IN STREPTOMYCES-LIVIDANS-66 AND THE LOSS OF ONE END OF THE LINEAR CHROMOSOME

Thirty-two 2-deoxygalactose-resistant mutants with DNA amplifications were isolated from Streptomyces lividans 66 strains carrying plasmid p MT664, which carries an agarase gene (dag A) and IS466. Thirty-one of the mutants carried amplified DNA sequences from a 70 kb region about 300 kb from one end of the linear chromosome in this species. In 28 of the mutants, all the wild-type sequences between the amplified region and the start of the 30 kb inverted repeat that forms the chromosome end were deleted. Thus, there appeared to be loss of one chromosome en d and its replacement by the DNA amplification. In some mutants there amplification of a previously characterised 5.7 kb sequence that lies about 600 kb from the other chromosome end was also noted.