Abstract：
:Type II DNA topoisomerases are ubiquitous ATP-dependent enzymes capable of transporting a DNA through a transient double-strand break in a second DNA segment. This enables them to untangle DNA and relax the interwound supercoils (plectonemes) that arise in twisted DNA. In vivo, they are responsible for untangling replicated chromosomes and their absence at mitosis or meiosis ultimately causes cell death. Here we describe a micromanipulation experiment in which we follow in real time a single Drosophila melanogaster topoisomerase II acting on a linear DNA molecule which is mechanically stretched and supercoiled. By monitoring the DNA's extension in the presence of ATP, we directly observe the relaxation of two supercoils during a single catalytic turnover. By controlling the force pulling on the molecule, we determine the variation of the reaction rate with the applied stress. Finally, in the absence of ATP, we observe the damping of a DNA crossover by a single topoisomerase on at least two different timescales (configurations). These results show that single molecule experiments are a powerful new tool for the study of topoisomerases.
journal_name
Naturejournal_title
Natureauthors
Strick TR,Croquette V,Bensimon Ddoi
10.1038/35009144keywords:
subject
Has Abstractpub_date
2000-04-20 00:00:00pages
901-4issue
6780eissn
0028-0836issn
1476-4687journal_volume
404pub_type
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