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Chromatin regulates DNA torsional energy via topoisomerase II-mediated relaxation of positive supercoils

AuthorsFernàndez, Xavier; Díaz-Ingelmo, Ofelia ; Martínez-García, Belén ; Roca, Joaquim
Issue Date23-May-2014
PublisherNature Publishing Group
CitationEMBO Journal 33(13): 1492-1501 (2014)
AbstractEukaryotic topoisomerases I (topo I) and II (topo II) relax the positive (+) and negative (-) DNA torsional stress (TS) generated ahead and behind the transcription machinery. It is unknown how this DNA relaxation activity is regulated and whether (+) and (-)TS are reduced at similar rates. Here, we used yeast circular minichromosomes to conduct the first comparative analysis of topo I and topo II activities in relaxing chromatin under (+) and (-)TS. We observed that, while topo I relaxed (+) and (-)TS with similar efficiency, topo II was more proficient and relaxed (+)TS more quickly than (-)TS. Accordingly, we found that the relaxation rate of (+)TS by endogenous topoisomerases largely surpassed that of (-)TS. We propose a model of how distinct conformations of chromatin under (+) and (-)TS may produce this unbalanced relaxation of DNA. We postulate that, while quick relaxation of (+)TS may facilitate the progression of RNA and DNA polymerases, slow relaxation of (-)TS may serve to favor DNA unwinding and other structural transitions at specific regions often required for genomic transactions. © 2014 The Authors.
Publisher version (URL)http://dx.doi.org/10.15252/embj.201488091
Identifiersdoi: 10.15252/embj.201488091
issn: 1460-2075
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