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Article
Subject Categories: Chromatin & Transcription | Genome Stability & Dynamics
The EMBO Journal (2006) 25, 3123–3132, doi:10.1038/sj.emboj.7601196
Published online 15 June 2006
Rapid accessibility of nucleosomal DNA in yeast on a second time scale
Andrea Bucceri, Kristin Kapitza and Fritz Thoma
Institut für Zellbiologie, ETH Zürich, Zürich, Switzerland

To whom correspondence should be addressed
Fritz Thoma, Institut für Zellbiologie, ETH Zürich, Hönggerberg, 8093 Zürich, Switzerland. Tel.: +41 44 633 3323; Fax: +41 44 633 1069; E-mail: thoma@cell.biol.ethz.ch

Received 15 February 2006; Accepted 22 May 2006; Published online 15 June 2006.
Abstract
Packaging DNA in nucleosomes and higher-order chromatin structures restricts its accessibility and constitutes a barrier for all DNA transactions including gene regulation and DNA repair. How and how fast proteins find access to DNA buried in chromatin of living cells is poorly understood. To address this question in a real time in vivo approach, we investigated DNA repair by photolyase in yeast. We show that overexpressed photolyase, a light-dependent DNA-repair enzyme, recognizes and repairs UV-damaged DNA within seconds. Rapid repair was observed in various nucleosomal regions of the genome including inactive and active genes and repressed promoters. About 50% of cyclobutane pyrimidine dimers were removed in 5 s, >80% in 90 s. Heterochromatin was repaired within minutes, centromeres were not repaired. Consistent with fast conformational transitions of nucleosomes observed in vitro, this rapid repair strongly suggests that spontaneous unwrapping of nucleosomes rather than histone dissociation or chromatin remodeling provides DNA access. The data impact our view on the repressive and dynamic nature of chromatin and illustrate how proteins like photolyase can access DNA in structurally and functionally diverse chromatin regions.
Keywords: chromatin, DNA repair, nucleosome, photolyase, yeast
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