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Analyse comparative de la dynamique de deux éléments intégratifs conjugatifs de streptococcus thermophilus

Abstract : Integrative and Conjugative Elements (ICEs) are genomic islands, which excise from the chromosome, self-transfer by conjugation and integrate. They harbor a modular organization: genes and sequences involved in the same biological process are grouped in the same region. This work concerns the modality of transfer and maintenance of ICESt1 and ICESt3, two ICEs of Streptococcus thermophilus that share closely related core region. ICESt1 excises much less frequently than ICESt3. Nevertheless, excision of the two elements is activated by the same stimuli (DNA damage, stationary phase and/or cell density) and depends of the host strain. Bioinformatical and transcriptional analyses highlight several differences in their organization. However, each of these two ICEs would encode two different regulators, cI and ImmR, suggesting that a complex and original pathway govern to ICESt1' and ICESt3' regulation. This regulation would be shared with numerous ICEs that we identified in the genome of various commensal or pathogenic streptococci. According to the original definition, ICE's maintenance would be exclusively due to their integration in the host chromosome, and ICEs would not be able of extracellular replication. However, in addition to the induction of ICESt3' excision and transfer, DNA damage cause replication of its extrachromosomal form. This unexpected property is encoded by the core region and would be implicated in the maintenance of the element. Comparision with data recently published on other ICEs suggest that intracellular replication could be involved in the maintenance of numerous ICEs, besides their integration.
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  • HAL Id : tel-01746210, version 1

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Nicolas Carraro. Analyse comparative de la dynamique de deux éléments intégratifs conjugatifs de streptococcus thermophilus. Génomique, Transcriptomique et Protéomique [q-bio.GN]. Université Henri Poincaré - Nancy 1, 2011. Français. ⟨NNT : 2011NAN10080⟩. ⟨tel-01746210⟩

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