Cell Reports
Volume 20, Issue 9, 29 August 2017, Pages 2057-2071
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Article
SMC Progressively Aligns Chromosomal Arms in Caulobacter crescentus but Is Antagonized by Convergent Transcription

https://doi.org/10.1016/j.celrep.2017.08.026Get rights and content
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Highlights

  • Caulobacter SMC aligns the two chromosomal arms progressively from ori to ter

  • SMC is loaded at parS, and ParB is essential for SMC-mediated arm alignment

  • SMC likely functions as a tether to cohese parS-proximal DNA together

  • Head-on transcription interferes with SMC translocation from parS

Summary

The structural maintenance of chromosomes (SMC) complex plays an important role in chromosome organization and segregation in most living organisms. In Caulobacter crescentus, SMC is required to align the left and the right arms of the chromosome that run in parallel down the long axis of the cell. However, the mechanism of SMC-mediated alignment of chromosomal arms remains elusive. Here, using genome-wide methods and microscopy of single cells, we show that Caulobacter SMC is recruited to the centromeric parS site and that SMC-mediated arm alignment depends on the chromosome-partitioning protein ParB. We provide evidence that SMC likely tethers the parS-proximal regions of the chromosomal arms together, promoting arm alignment. Furthermore, we show that highly transcribed genes near parS that are oriented against SMC translocation disrupt arm alignment, suggesting that head-on transcription interferes with SMC translocation. Our results demonstrate a tight interdependence of bacterial chromosome organization and global patterns of transcription.

Keywords

chromosome organization
structural maintenance of chromosomes
SMC
Hi-C
ChIP-seq
head-on transcription conflicts
chromosome segregation
ParB
parS
Caulobacter

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