These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Topoisomerase II, not topoisomerase I, is the proficient relaxase of nucleosomal DNA.
    Author: Salceda J, Fernández X, Roca J.
    Journal: EMBO J; 2006 Jun 07; 25(11):2575-83. PubMed ID: 16710299.
    Abstract:
    Eukaryotic topoisomerases I and II efficiently remove helical tension in naked DNA molecules. However, this activity has not been examined in nucleosomal DNA, their natural substrate. Here, we obtained yeast minichromosomes holding DNA under (+) helical tension, and incubated them with topoisomerases. We show that DNA supercoiling density can rise above +0.04 without displacement of the histones and that the typical nucleosome topology is restored upon DNA relaxation. However, in contrast to what is observed in naked DNA, topoisomerase II relaxes nucleosomal DNA much faster than topoisomerase I. The same effect occurs in cell extracts containing physiological dosages of topoisomeraseI and II. Apparently, the DNA strand-rotation mechanism of topoisomerase I does not efficiently relax chromatin, which imposes barriers for DNA twist diffusion. Conversely, the DNA cross-inversion mechanism of topoisomerase II is facilitated in chromatin, which favor the juxtaposition of DNA segments. We conclude that topoisomerase II is the main modulator of DNA topology in chromatin fibers. The nonessential topoisomerase I then assists DNA relaxation where chromatin structure impairs DNA juxtaposition but allows twist diffusion.
    [Abstract] [Full Text] [Related] [New Search]