Chromatin remodelers are complexes able to both alter histone-DNA interactions and to mobilize nucleosomes. The mechanism of their action and the conformation of remodeled nucleosomes remain a matter of debates. In this work we compared the type and structure of the products of nucleosome remodeling by SWI/SNF and ACF complexes using high-resolution microscopy combined with novel biochemical approaches. We find that SWI/SNF generates a multitude of nucleosome-like metastable particles termed "remosomes". Restriction enzyme accessibility assay, DNase I footprinting and AFM experiments reveal perturbed histone-DNA interactions within these particles. Electron cryo-microscopy shows that remosomes adopt a variety of different structures with variable irregular DNA path, similar to those described upon RSC remodeling. Remosome DNA accessibility to restriction enzymes is also markedly increased. We suggest that the generation of remosomes is a common feature of the SWI/SNF family remodelers. In contrast, the ACF remodeler, belonging to ISWI family, only produces repositioned nucleosomes and no evidence for particles associated with extra DNA, or perturbed DNA paths was found. The remosome generation by the SWI/SNF type of remodelers may represent a novel mechanism involved in processes where nucleosomal DNA accessibility is required, such as DNA repair or transcription regulation.

Cellule LBMC 46 Allée d'Italie 69007 Lyon France

Institut de Génétique et de Biologie Moléculaire et Cellulaire CNRS INSERM ULP Parc d'innovation 1 rue Laurent Fries 67404 Ilkirch Cedex France

Izmir Biomedicine and Genome Center Izmir Turkey

Laboratoire de Physique UMR 5672 CNRS Université de Lyon 1 Ecole Normale Supérieure de Lyon 69364 Lyon cedex 07 France

Laboratory of the Biology and Pathology of the Eye Institute of Biology and Medical Genetics and Institute of Medical Biochemistry and Laboratory Diagnostics 1st Faculty of Medicine Charles University and General University Hospital Prague Albertov 4 128 00 Prague 2 Czech Republic

MRC Laboratory of Molecular Biology Hills Road Cambridge CB2 2QH UK

Pharmacology Division CSIR IIIM Sanatnagar Srinagar 190005 Jammu and Kashmir India

Université de Lyon Laboratoire de Biologie et Modélisation de la Cellule CNRS UMR 5239 Ecole Normale Supérieure de Lyon 46 Allée d'Italie 69364 Lyon cedex 07 France

Université Grenoble Alpes CNRS UMR 5309 INSERM U1209 Institute for Advanced Biosciences Site Santé Allée des Alpes 38700 La Tronche France

Wellcome Centre for Cell Biology and Institute of Cell Biology School of Biological Sciences The University of Edinburgh Swann Building King's Buildings Mayfield Road Edinburgh EH9 3BF United Kingdom

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