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Originally published in Science Express on 3 June 2004
Science 9 July 2004:
Vol. 305. no. 5681, pp. 222 - 227
DOI: 10.1126/science.1098225
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Research Articles

This article has been retracted

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

Ryan B. Case,1,2* Yun-Pei Chang,3* Steven B. Smith,2,4 Jeff Gore,2 Nicholas R. Cozzarelli,1,3{dagger} Carlos Bustamante1,2,3,4{dagger}

Condensins are conserved proteins containing SMC (structural maintenance of chromosomes) moieties that organize and compact chromosomes in an unknown mechanism essential for faithful chromosome partitioning. We show that MukBEF, the condensin in Escherichia coli, cooperatively compacts a single DNA molecule into a filament with an ordered, repetitive structure in an adenosine triphosphate (ATP) binding–dependent manner. When stretched to a tension of ~17 piconewtons, the filament extended in a series of repetitive transitions in a broad distribution centered on 45 nanometers. A filament so extended and held at a lower force recondensed in steps of 35 nanometers 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 was identical in every subsequent extension. Hence, after being deformed micrometers in length, each filament returned to its original compact structure without the addition of energy. Incubation with topoisomerase I increased the rate of recondensation and allowed 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.

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



* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: ncozzare{at}socrates.berkeley.edu (N.R.C.), carlos{at}alice.berkeley.edu (C.B.)

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