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Genes Dev. 2015 Aug 1;29(15):1661-75. doi: 10.1101/gad.265876.115.

Condensin promotes the juxtaposition of DNA flanking its loading site in Bacillus subtilis.

Author information

1
Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts 02115, USA;
2
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
3
Program in Systems Biology, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA;
4
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Abstract

SMC condensin complexes play a central role in compacting and resolving replicated chromosomes in virtually all organisms, yet how they accomplish this remains elusive. In Bacillus subtilis, condensin is loaded at centromeric parS sites, where it encircles DNA and individualizes newly replicated origins. Using chromosome conformation capture and cytological assays, we show that condensin recruitment to origin-proximal parS sites is required for the juxtaposition of the two chromosome arms. Recruitment to ectopic parS sites promotes alignment of large tracks of DNA flanking these sites. Importantly, insertion of parS sites on opposing arms indicates that these "zip-up" interactions only occur between adjacent DNA segments. Collectively, our data suggest that condensin resolves replicated origins by promoting the juxtaposition of DNA flanking parS sites, drawing sister origins in on themselves and away from each other. These results are consistent with a model in which condensin encircles the DNA flanking its loading site and then slides down, tethering the two arms together. Lengthwise condensation via loop extrusion could provide a generalizable mechanism by which condensin complexes act dynamically to individualize origins in B. subtilis and, when loaded along eukaryotic chromosomes, resolve them during mitosis.

KEYWORDS:

DNA segregation; Hi-C; ParB; SMC; lengthwise condensation; mitosis; parS

PMID:
26253537
PMCID:
PMC4536313
DOI:
10.1101/gad.265876.115
[Indexed for MEDLINE]
Free PMC Article

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