Cell
Volume 175, Issue 2, 4 October 2018, Pages 583-597.e23
Journal home page for Cell

Article
A Bacterial Chromosome Structuring Protein Binds Overtwisted DNA to Stimulate Type II Topoisomerases and Enable DNA Replication

https://doi.org/10.1016/j.cell.2018.08.029Get rights and content
Under an Elsevier user license
open archive

Highlights

  • GapR is a DNA structuring protein conserved throughout α-proteobacteria

  • GapR promotes DNA replication initiation and elongation

  • GapR encircles overtwisted DNA as a dimer-of-dimers

  • GapR stimulates the relaxation of positive supercoils by gyrase and topo IV

Summary

When DNA is unwound during replication, it becomes overtwisted and forms positive supercoils in front of the translocating DNA polymerase. Unless removed or dissipated, this superhelical tension can impede replication elongation. Topoisomerases, including gyrase and topoisomerase IV in bacteria, are required to relax positive supercoils ahead of DNA polymerase but may not be sufficient for replication. Here, we find that GapR, a chromosome structuring protein in Caulobacter crescentus, is required to complete DNA replication. GapR associates in vivo with positively supercoiled chromosomal DNA, and our biochemical and structural studies demonstrate that GapR forms a dimer-of-dimers that fully encircles overtwisted DNA. Further, we show that GapR stimulates gyrase and topo IV to relax positive supercoils, thereby enabling DNA replication. Analogous chromosome structuring proteins that locate to the overtwisted DNA in front of replication forks may be present in other organisms, similarly helping to recruit and stimulate topoisomerases during DNA replication.

Keywords

supercoiling
DNA replication
gyrase
topoisomerase IV
type IIA topoisomerases
chromosome organization
DNA topology
nucleoid-associated proteins
GapR
Caulobacter crescentus

Cited by (0)

4

These authors contributed equally

5

Present address: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA

6

Lead Contact