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Journal of Bacteriology, October 2007, p. 7062-7068, Vol. 189, No. 19
0021-9193/07/$08.00+0     doi:10.1128/JB.00770-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

MukEF Is Required for Stable Association of MukB with the Chromosome{triangledown}

Weifeng She, Qinhong Wang, Elena A. Mordukhova, and Valentin V. Rybenkov*

Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, Oklahoma 73019

Received 17 May 2007/ Accepted 10 July 2007

MukB is a bacterial SMC(structural maintenance of chromosome) protein required for correct folding of the Escherichia coli chromosome. MukB acts in complex with the two non-SMC proteins, MukE and MukF. The role of MukEF is unclear. MukEF disrupts MukB-DNA interactions in vitro. In vivo, however, MukEF stimulates MukB-induced DNA condensation and is required for the assembly of MukB clusters at the quarter positions of the cell length. We report here that MukEF is essential for stable association of MukB with the chromosome. We found that MukBEF forms a stable complex with the chromosome that copurifies with nucleoids following gentle cell lysis. Little MukB could be found with the nucleoids in the absence or upon overproduction of MukEF. Similarly, overproduced MukEF recruited MukB-green fluorescent protein (GFP) from its quarter positions, indicating that formation of MukB-GFP clusters and stable association with the chromosome could be mechanistically related. Finally, we report that MukE-GFP forms foci at the quarter positions of the cell length but not in cells that lack MukB or overproduce MukEF, suggesting that the clusters are formed by MukBEF and not by its individual subunits. These data support the view that MukBEF acts as a macromolecular assembly, a scaffold, in chromosome organization and that MukEF is essential for the assembly of this scaffold.

* Corresponding author. Mailing address: Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, OK 73019. Phone: (405) 325-1677. Fax: (405) 325-6111. E-mail: valya{at}ou.edu

{triangledown} Published ahead of print on 20 July 2007.

Journal of Bacteriology, October 2007, p. 7062-7068, Vol. 189, No. 19
0021-9193/07/$08.00+0     doi:10.1128/JB.00770-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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