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Dynamique des extrémités du chromosome linéaire de Streptomyces ambofaciens

Abstract : The Streptomyces are soil bacteria with a large linear chromosome, typically 8 to 10 Mb, high part of G-C bases (72.1% for S. coelicolor) and are subject to a high degree of genetic instability, correlated with the formation of large rearrangement occurring in the terminal chromosomal regions. The analysis of the terminal regions sequences and partial sequence central region of S. ambofaciens ATCC23877 shows that the size of the terminal species-specific regions increases as the phylogenetic distance between compared species increases. The synteny observed between central regions degenerates progressively over several hundreds of kilobases before reaching the terminal species-specific regions. This synteny appears as gradually parceled out by multiple insertions/deletions (indels) of genes. The comparison of the sequences of the Terminal Inverted Repeat (TIR) of two S. ambofaciens strains shows the two strains share the same ancestral boundaries of TIRs. On the other hand, the terminals regions are strain-specific suggesting that exchanges of replicon extremities, potentially plasmidic, have occurred, contributing to the terminal variability observed at the intraspecific level. The mechanisms of double breaks repair or the frequency of these double breaks could be the reasons of this variability. Sometimes, the chromosome becomes dicentric and enters in a break-fusion-bridge (BFB) cycle. This cycle is the consequence of a end-to-end fusion of two deleted chromosomes. The analysis of S. ambofaciens DSM40697 strains with a second locus involved in the partitioning narrows the implication of this one in the chromosomic instability and the Streptomyces' evolution.
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  • HAL Id : tel-01748260, version 1

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Alexandre Gallois. Dynamique des extrémités du chromosome linéaire de Streptomyces ambofaciens. Génétique. Université Henri Poincaré - Nancy 1, 2007. Français. ⟨NNT : 2007NAN10108⟩. ⟨tel-01748260⟩

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