title: End-to-end fusion of linear deleted chromosomes initiates a cycle of genome instability in Streptomyces ambofaciens.
abstract: Two mutant strains harbouring a linear chromosome whose size reached 13 Mb (versus approximately 8 Mb for the wild type) were characterized. This chromosomal structure resulted from the fusion in inverted orientation of two chromosomes partially deleted on the same arm. The fusion occurred by illegitimate recombination between 6 bp repeats. This chromosomal structure was inherited in strict association with a high level of genetic instability (30% of mutants in a single progeny, phenomenon also called hypervariability) and chromosomal instability. In contrast, derivatives, which did not retain the chromosome fusion, showed a wild-type-like instability frequency (c. 1%). Stabilization of the chromosomal structure occurred by chromosome arm replacement or circularization. A high variability of the terminal inverted repeat (TIR) length in the rescued chromosomes (from 5 kb to approximately 1.4 Mb for linear derivatives) was observed. Mutant lineages harbouring the chromosomal fusion are characterized by a highly heterogeneous distribution of DNA in the spores, by the presence of spores without DNA as well as aberrant sporulation figures, and by the production of spores with a low germination rate. The wild-type characteristics were restored in the descendants, which lost the chromosomal fusion. Thus, the fusion of deleted chromosomes initiates a cycle of chromosome instability sharing several levels of analogy with the behaviour of dicentric chromosomes in eukaryotes. We propose that the high instability of the fused chromosomes results from the duplication of a region involved in partitioning of the chromosomes (parAB-oriC ).
authors: Génétique et Microbiologie UMR INRA - UHP 1128, IFR110, Faculté des Sciences et Techniques, Université Henri Poincaré-Nancy 1, Boulevard des Aiguillettes BP 239, 54506 Vandoeuvre-lès-Nancy, France.
authors: Thomas
authors: T
authors: Wenner
authors: Virginie
authors: V
authors: Roth
authors: Gilles
authors: G
authors: Fischer
authors: Céline
authors: C
authors: Fourrier
authors: Bertrand
authors: B
authors: Aigle
authors: Bernard
authors: B
authors: Decaris
authors: Pierre
authors: P
authors: Leblond
mesh_terms: D002876:Chromosomes, Bacterial; D004269:DNA, Bacterial / Q000235:genetics*; D015321:Gene Rearrangement; D016680:Genome, Bacterial; D042822:Genomic Instability; D009154:Mutation; D011995:Recombination, Genetic; D013302:Streptomyces / Q000235:genetics* / Q000254:growth & development
chemical_list: D004269:DNA, Bacterial