Extremely large chromosomal deletions are intimately involved in genetic instability and genomic rearrangements in Streptomyces glaucescens

Abstract

Genetic instability in Streptomyces glaucescens characteristically involves the occurrence of gross genomic rearrangements including high-level sequence amplification and extensive deletion. We investigated the relationship of the unstable melC and strS loci and a 100 kb region of the chromosome which frequently gives rise to intense heterogeneous DNA amplification. Standard chromosome walking using a cosmid bank in conjunction with a "reverse-blot" procedure enabled us to construct a contiguous genomic BamHI map of the unstable region exceeding 900 kb. The unstable genes and the amplifiable region (AUD locus) are physically linked within a 600 kb segment of the chromosome. The previously characterized deletions which affect these loci are merely components of much larger deletions ranging from 270 to over 800 kb which are polar in nature, effecting the sequential loss of the strS and melC loci. The more extensive deletions terminate either adjacent to, or in the vicinity of DNA reiterations at the AUD locus. Additionally, a deletion junction fragment and the corresponding deletion ends were cloned and analysed at the sequence level.