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Segrosome structure revealed by a complex of ParR with centromere DNA


The stable inheritance of genetic material depends on accurate DNA partition. Plasmids serve as tractable model systems to study DNA segregation because they require only a DNA centromere, a centromere-binding protein and a force-generating ATPase. The centromeres of partition (par) systems typically consist of a tandem arrangement of direct repeats1,2,3,4,5,6,7. The best-characterized par system contains a centromere-binding protein called ParR and an ATPase called ParM. In the first step of segregation, multiple ParR proteins interact with the centromere repeats to form a large nucleoprotein complex of unknown structure called the segrosome, which binds ParM filaments4,8,9,10. pSK41 ParR binds a centromere consisting of multiple 20-base-pair (bp) tandem repeats to mediate both transcription autoregulation and segregation. Here we report the structure of the pSK41 segrosome revealed in the crystal structure of a ParR–DNA complex. In the crystals, the 20-mer tandem repeats stack pseudo-continuously to generate the full-length centromere with the ribbon–helix–helix (RHH) fold of ParR binding successive DNA repeats as dimer-of-dimers. Remarkably, the dimer-of-dimers assemble in a continuous protein super-helical array, wrapping the DNA about its positive convex surface to form a large segrosome with an open, solenoid-shaped structure, suggesting a mechanism for ParM capture and subsequent plasmid segregation.

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Figure 1: The pSK41 centromere-like site.
Figure 2: Structure of pSK41 ParR–DNA segrosome.
Figure 3: ParR–DNA and ParR–ParR interactions in the segrosome.
Figure 4: pSK41 segregation model.


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We thank the Advanced Light Source (ALS) and their support staff. The ALS is supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences Division of the US Department of Energy at the Lawrence Berkeley National Laboratory. We also thank Dr S. Kwong for supplying shuttle vectors and Professor K. Gerdes for pointing out the presence of the pSK41 par system. This work was supported by a Burroughs Wellcome Career Development Award, a U.T. M.D. Anderson Trust Fellowship and a National Institutes of Health grant (to M.A.S.), an Australian Research Council Grant (to N.F. and R.A.S.) and a National Health and Medical Research Council (Australia) Project Grant (to R.A.S. and N.F.).

Author Contributions M.A.S. performed the crystallographic studies, fluorescence polarization, oversaw cryo-electron microscopy studies and wrote the manuscript. T.C.G. generated ParRN and ParRC constructs. T.D.D. performed cryo-electron microscopy studies. A.J.B. generated plasmid constructs and undertook the regulatory and functional studies. S.O.J. performed the electrophoretic mobility shift assays (EMSA) and footprinting assays and contributed to the manuscript. R.A.S. and N.F. conceived and oversaw the functional studies and contributed to the manuscript.

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Correspondence to Maria A. Schumacher.

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Supplementary Information

The file contains Supplementary Discussion describing the clinical relevance of the pSK41 par system. This section also provides more in depth discussion regarding the CAT assays, DNase I protection and cryo-EM studies. Also included, there are Supplementary Figures 1-6 with Legends and Supplementary Tables 1-2. (PDF 1109 kb)

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Schumacher, M., Glover, T., Brzoska, A. et al. Segrosome structure revealed by a complex of ParR with centromere DNA. Nature 450, 1268–1271 (2007).

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