SMC condensin entraps chromosomal DNA by an ATP hydrolysisdependent loading mechanism in Bacillus subtilis

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Abstract

Smc-ScpAB forms elongated, annular structures that promote chromosome segregation, presumably by compacting and resolving sister DNA molecules. The mechanistic basis for its action, however, is only poorly understood. Here, we have established a physical assay to determine whether the binding of condensin to native chromosomes in Bacillus subtilis involves entrapment of DNA by the Smc-ScpAB ring. To do so, we have chemically cross-linked the three ring interfaces in Smc-ScpAB and thereafter isolated intact chromosomes under protein denaturing conditions. Exclusively species of Smc-ScpA, which were previously cross-linked into covalent rings, remained associated with chromosomal DNA. DNA entrapment is abolished by mutations that interfere with the Smc ATPase cycle and strongly reduced when the recruitment factor ParB is deleted, implying that most Smc-ScpAB is loaded onto the chromosome at parS sites near the replication origin. We furthermore report a physical interaction between native Smc-ScpAB and chromosomal DNA fragments.

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Larissa Wilhelm

Chromosome Organization and Dynamics, Max Planck Institute of Biochemistry, Martinsried, Germany

Competing interests
The authors declare that no competing interests exist.
Frank Bürmann

Chromosome Organization and Dynamics, Max Planck Institute of Biochemistry, Martinsried, Germany

Competing interests
The authors declare that no competing interests exist.
Anita Minnen

Chromosome Organization and Dynamics, Max Planck Institute of Biochemistry, Martinsried, Germany

Competing interests
The authors declare that no competing interests exist.
Ho-Chul Shin

Functional Genomics Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea

Competing interests
The authors declare that no competing interests exist.
Christopher P Toseland

Chromosome Organization and Dynamics, Max Planck Institute of Biochemistry, Martinsried, Germany

Competing interests
The authors declare that no competing interests exist.
Byung-Ha Oh

Department of Biological Sciences, KAIST Institute for the Biocentury, Cancer Metastasis Control Center, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea

Competing interests
The authors declare that no competing interests exist.
Stephan Gruber

Chromosome Organization and Dynamics, Max Planck Institute of Biochemistry, Martinsried, Germany

For correspondence
sgruber@biochem.mpg.de

Competing interests
The authors declare that no competing interests exist.

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