Sur ce site

Sur le Web du CNRS

Accueil du site > Animations Scientifiques > Séminaires 2007 > Histone H1 is a architectural molecule required for chromatin compaction, and is redundant for gene repression

Histone H1 is a architectural molecule required for chromatin compaction, and is redundant for gene repression

Orateur :

Hugh Patterton, Laboratory of Epigenomics and DNA Function, Department of Biotechnology, University of the Free State, Bloemfontein, South Africa

Salle :


Sujet :

The linker histone binds to the outside of the nucleosome core, straddling two gyres of nucleosomal DNA at the entry/exit points of the nucleosome, and contacting the DNA close to the dyad axis and within the last helical turn of the nucleosome. The yeast Saccharomyces cerevisiae, a unicellular eukaryote, contains a single copy of the linker histone, Hho1p. This linker histone is unusual in that it contains two single winged helix motif globular domains, separated by a lysine-rich region. We have shown that Hho1p can bind to two four-way junction DNA molecules simultaneously, suggesting that Hho1p may contact two adjacent nucleosomes when bound to chromatin.

We have also shown that, although the level of Hho1p protein remained constant from exponential phase to stationary phase, Hho1p binds to chromatin preferentially during stationary phase. Microarray analysis of gene expression in stationary phase showed that all genes were expressed at significantly lower levels and that this genome-wide repression did nor require Hho1p. Further microarray analysis at 15min, 30min, 1h and 2h time points showed that although the genes on some chromosomes became activated in domains, no similar Hho1p-dependent domains could be identified, suggesting that Hho1p was not involved in domain-wide gene regulation. We next performed a chip-on-chip analysis, and showed that Hho1p was evenly distributed throughout the genome in stationary phase. There was no evidence for the preferential binding of Hho1p to AT-rich regions or silenced regions during exponential phase. We also investigated chromatin compaction in stationary and exponential phase in a genome-wide fashion, and showed that chromatin was evenly compacted during stationary phase, and that this compaction required the presence of Hho1p.

Dans la même rubrique :