Multiple cis-Acting rDNAs Contribute to Nucleoid Separation and Recruit the Bacterial Condensin Smc-ScpAB

Cell Rep. 2017 Oct 31;21(5):1347-1360. doi: 10.1016/j.celrep.2017.10.014.


Condensins load onto DNA to organize chromosomes. Smc-ScpAB clearly loads onto the parS sites bound by Spo0J, but other loading site(s) must operate independently of parS. In this study, we asked where and how Smc-ScpAB normally selects its loading site. Our results suggest that rDNA is also a loading site. A pull-down assay revealed that Smc-ScpAB preferentially loads onto rDNA in the wild-type cell and even in a Δspo0J mutant but not in a Δsmc mutant. Moreover, we showed that deletion mutants of rDNAs cause a defect in nucleoid separation, and at least two rDNAs near oriC are essential for separation. Full-length rDNA, including promoters, is required for loading and nucleoid separation. A synthetic defect by deletions of both rDNA and spo0J resulted in more aberrant nucleoid separation. We propose that a single-stranded segment of DNA that is exposed at highly transcribed rRNA operons would become a target for Smc-ScpAB loading.

Keywords: R-loop; Smc; bacteria; chromosome; oriC resolution; pull-down; single-stranded DNA; topological binding; transcription.

MeSH terms

  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / metabolism*
  • Bacillus subtilis / genetics
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism
  • Cell Nucleolus / genetics
  • Cell Nucleolus / metabolism
  • DNA, Ribosomal / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism*
  • Mutagenesis
  • Plasmids / metabolism


  • Bacterial Proteins
  • Cell Cycle Proteins
  • DNA, Ribosomal
  • DNA-Binding Proteins
  • Multiprotein Complexes
  • ScpA protein, Bacillus subtilis
  • condensin complexes
  • spore-specific proteins, Bacillus
  • Adenosine Triphosphatases