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Chromatin regulates DNA torsional energy via topoisomerase II‐mediated relaxation of positive supercoils
Author(s) -
Fernández Xavier,
DíazIngelmo Ofelia,
MartínezGarcía Belén,
Roca Joaquim
Publication year - 2014
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.15252/embj.201488091
Subject(s) - topoisomerase , dna supercoil , biology , chromatin , dna , transcription (linguistics) , relaxation (psychology) , biophysics , rna , microbiology and biotechnology , genetics , dna replication , gene , linguistics , philosophy , neuroscience
Eukaryotic 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.