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Published Online June 3, 2004
Science DOI: 10.1126/science.1098225

Research Articles

This article has been retracted

Submitted on March 23, 2004
Accepted on May 20, 2004

The Bacterial Condensin MukBEF Compacts DNA into a Repetitive, Stable Structure

Ryan B. Case 1, Yun-Pei Chang 2, Steven B. Smith 3, Jeff Gore 4, Nicholas R. Cozzarelli 5*, Carlos Bustamante 6*

1 Department of Molecular and Cell Biology; Department of Physics, University of California, Berkeley, CA 94720, USA.
2 Biophysics Graduate Group, University of California, Berkeley, CA 94720, USA.
3 Department of Physics; Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA.
4 Department of Physics, University of California, Berkeley, CA 94720, USA.
5 Department of Molecular and Cell Biology; Biophysics Graduate Group, University of California, Berkeley, CA 94720, USA.
6 Department of Molecular and Cell Biology; Department of Physics; Biophysics Graduate Group; Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA.

* To whom correspondence should be addressed.
Nicholas R. Cozzarelli , E-mail: ncozzare{at}socrates.berkeley.edu
Carlos Bustamante , E-mail: carlos{at}alice.berkeley.edu

Condensins are conserved proteins containing Structural Maintenance of Chromosomes (SMC) moieties that organize and compact chromosomes in an unknown mechanism essential for faithful chromosome partitioning. We show that MukBEF, the condensin in Escherichia coli, compacts cooperatively a single DNA molecule into a filament with an ordered, repetitive structure in an ATP binding-dependent manner. When stretched to a tension of ~ 17 pN, the filament extended in a series of repetitive transitions in a broad distribution centered on 45 nm. A filament so extended and held at a lower force recondensed in steps of 35 nm or its multiples; this cycle was repeatable even in the absence of ATP and free MukBEF. Remarkably, the pattern of transitions displayed by a given filament during the initial extension reproduced identically in every subsequent extension. Hence, after being deformed microns in length each filament returns to its original compact structure without the addition of energy. Incubation with topoisomerase I increased the rate of recondensation, allowing the structure to extend and reform almost reversibly, indicating that supercoiled DNA is trapped in the condensed structure. We suggest a new model for how MukBEF organizes the bacterial chromosome in vivo.


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