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Chromatin : from structure to epigenetic properties

Vendredi 7 mars 2014 11:00 - Duree : 1 heure
Lieu : Salle des séminaires de l’IBS - 6 rue Jules Horowitz - Grenoble

Orateur : Stefan DIMITROV (Institut Albert Bonniot, Grenoble)

DNA in the cell nucleus is organized into chromatin. Chromatin impedes the binding of protein factors to the underlying DNA sequences. The cell uses three main “tools” to overcome the chromatin barrier, namely : chromatin remodelers, histone variants and histone post-translational modifications. We will give specific examples of how either one of these “tools” function. Chromatin remodelers are sophisticated nano-machines, which are able to alter histone-DNA interactions and to mobilize nucleosomes. Neither the mechanism of their action nor the conformation of the remodeled nucleosomes are, however, yet well understood. We have studied the mechanism of RSC-induced chromatin remodeling by using high resolution microscopy and state of the art biochemistry techniques. The data illustrates how RSC remodels the nucleosome in vitro and shed light on its in vivo function. CENP-A is a histone H3 variant, which replaces conventional histone H3 at centromeres and is a universal epigenetic centromeric marker. The NH2-terminus of human CENP-A is phosphorylated at serine 7 during mitosis but the role of this phosphorylation remains elusive. We have deciphered the in vivo function of CENP-A NH2-terminus. Our data reveals why the phosphorylation of CENP-A is required for mitosis. The crystal structure of the CENP-A nucleosome was recently solved. Intriguingly, in contrast to the canonical nucleosome (where 147 bp of DNA are wrapped around the histone octamer), only the central 121 bp were visible, suggesting flexible CENP-A nucleosomal ends. Why the CENP-A nucleosome exhibits flexible DNA ends is totally unknown. We will present data demonstrating that the more flexible DNA ends of the CENP-A nucleosome are required for its mitotic functions. We were able to “rigidify” the ends of the CENP-A nucleosomes in vivo, which results, in turn, in strong both mitotic and cytokinetic effects associated with the mislocalization of specific protein factors. Our data illustrate how the cell uses the distinct CENP-A nucleosome conformation to control mitosis and cytokinesis.

Contact : odile.kaikati@ibs.fr

Discipline évènement : (Biologie / Chimie)
Entité organisatrice : (IBS)
Nature évènement : (Séminaire)
Evènement répétitif : (Séminaire IBS)
Site de l'évènement : Polygone scientifique

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