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

Elife. 2015 May 7:4:e06659. doi: 10.7554/eLife.06659.


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.

Keywords: B. subtilis; ParB protein; Smc proteins; biochemistry; chromosome condensation; chromosome segregation; chromosomes; condensin; genes; sliding clamp.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / metabolism*
  • Adenosine Triphosphate / biosynthesis*
  • Bacillus subtilis
  • Bacterial Proteins / metabolism*
  • Cell Cycle Proteins / metabolism*
  • Chromosomes, Bacterial / genetics*
  • DNA, Bacterial / metabolism*
  • DNA-Binding Proteins / metabolism*
  • Hydrolysis
  • Multiprotein Complexes / metabolism*


  • Bacterial Proteins
  • Cell Cycle Proteins
  • DNA, Bacterial
  • DNA-Binding Proteins
  • Multiprotein Complexes
  • SMC protein, Bacteria
  • condensin complexes
  • Adenosine Triphosphate
  • Adenosine Triphosphatases