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Accueil > Séminaires

Salle de réunion bat. HERBIER

Jeudi 05/11/15 - 11h

Andrew Travers, MRC Laboratory of Molecular Biology, Cambridge, UK.

"DNA superhelicity shapes genome organization and chromatin structure"

In a closed topological domain an active DNA translocase, such as RNA polymerase, generates positive and negative DNA superhelicity, respectively preceding and following its passage. The superhelicity so produced is not uniformly distributed along DNA but is likely highest closest to the active enzyme. Importantly some DNA sequences are more sensitive to topological strain than others. Short topologically sensitive sequences if bounded by insensitive sequences, as in some promoter sites, act as sinks for negative superhelicity facilitating local melting while longer sensitive sequences facilitate further coiling of DNA into a superhelix (writhing). The talk will describe how the DNA sequences of yeast and bacterial genes and of bacterial chromosomes functionally reflect varying levels of DNA superhelicity, implying that DNA superhelicity per se is a major determinant of sequence organization in genomes.

Chromatin selectively stores negative, but not positive, supercoils. In eukaryotic chromatin the 30 nm fibre is an iconic structure that constrains negative supercoils. I shall describe a novel structural model for this fibre that reconciles previously contradictory interpretations and is topologically consistent with all published data. I shall argue that this fibre, as is also characteristic of bacterial chromatin, is well suited to maintaining DNA compaction in a torsionally dynamic environment