Nucleosome eviction in mitosis assists condensin loading and chromosome condensation. (6th June 2016) - Toselli‐Mollereau, Esther
Abstract: Condensins associate with DNA and shape mitotic chromosomes. Condensins are enriched nearby highly expressed genes during mitosis, but how this binding is achieved and what features associated with transcription attract condensins remain unclear. Here, we report that condensin accumulates at or in the immediate vicinity of nucleosome‐depleted regions during fission yeast mitosis. Two transcriptional coactivators, the Gcn5 histone acetyltransferase and the RSC chromatin‐remodelling complex, bind to promoters adjoining condensin‐binding sites and locally evict nucleosomes to facilitate condensin binding and allow efficient mitotic chromosome condensation. The function of Gcn5 is closely linked to condensin positioning, since neither the localization of topoisomerase II nor that of the cohesin loader Mis4 is altered in gcn5 mutant cells. We propose that nucleosomes act as a barrier for the initial binding of condensin and that nucleosome‐depleted regions formed at highly expressed genes by transcriptional coactivators constitute access points into chromosomes where condensin binds free genomic DNA. Synopsis: Fission yeast condensin accumulates at nucleosome‐depleted regions in the vicinity of highly expressed genes. Nucleosomes hinder condensin localization, and their eviction coupled with transcription seems a key feature of condensin‐binding sites. Condensin accumulates at nucleosome‐depleted regions during mitosis in fission yeast. Nucleosome eviction by transcriptional co‐activators such as Gcn5, Mst2 and RSC is necessary for condensin binding and proper chromosome condensation. Nucleosome constitutes an obstacle for condensin localization. The presence of free, non‐nucleosomal DNA might be an important feature of condensin‐binding sites in eukaryotes. Abstract : Fission yeast condensin accumulates at nucleosome‐depleted regions in the vicinity of highly expressed genes, implying the nucleosomes hinder condensin binding.