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Curr Biol. 2004 May 25;14(10):874-80.

Real-time detection of single-molecule DNA compaction by condensin I.

Author information

1
Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA. strick@cshi.edu

Abstract

BACKGROUND:

Condensin is thought to contribute to large-scale DNA compaction during mitotic chromosome assembly. It remains unknown, however, how the complex reconfigures DNA structure at a mechanistic level.

RESULTS:

We have performed single-molecule DNA nanomanipulation experiments to directly measure in real-time DNA compaction by the Xenopus laevis condensin I complex. Condensin can bind to the nanomanipulated DNA in the absence of ATP, but it compacts the DNA only in the presence of hydrolyzable ATP. Linear compaction is evidenced by a reduction in the end-to-end extension of nanomanipulated DNA. The reaction results in total compaction of the DNA (i.e., zero end-to-end extension). Discrete and reversible DNA compaction events are observed in the presence of competitor DNA when the DNA is subjected to weak stretching forces (F = 0.4 picoNewton [pN]). The distribution of step sizes is broad and displays a peak at approximately 60 nm ( approximately 180 bp) as well as a long tail. This distribution is essentially unaffected by the topological state of the DNA substrate. Increasing the force to F = 10 pN drives the system toward step-wise reversal of compaction. The distribution of step sizes observed upon disruption of condensin-DNA interactions displays a sharp peak at approximately 30 nm ( approximately 90 bp) as well as a long tail stretching out to hundreds of nanometers.

CONCLUSIONS:

The DNA nanomanipulation assay allows us to demonstrate for the first time that condensin physically compacts DNA in an ATP-hydrolysis-dependent manner. Our results suggest that the condensin complex may induce DNA compaction by dynamically and reversibly introducing loops along the DNA.

PMID:
15186743
DOI:
10.1016/j.cub.2004.04.038
[Indexed for MEDLINE]
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