The bacterial DnaC helicase loader is a DnaB ring breaker

Ernesto Arias-Palomo, Valerie L. O'Shea, Iris V. Hood, James M. Berger

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


Dedicated AAA+ ATPases deposit hexameric ring-shaped helicases onto DNA to promote replication in cellular organisms. To understand how loading occurs, we used electron microscopy and small angle X-ray scattering (SAXS) to determine the ATP-bound structure of the intact E. coli DnaBṡDnaC helicase/loader complex. The 480 kDa dodecamer forms a three-tiered assembly, in which DnaC adopts a spiral configuration that remodels N-terminal scaffolding and C-terminal motor regions of DnaB to produce a clear break in the helicase ring. Surprisingly, DnaC's AAA+ fold is dispensable for ring remodeling because the DnaC isolated helicase-binding domain can both load DnaB onto DNA and increase the efficiency by which the helicase acts on substrates in vitro. Our data demonstrate that DnaC opens DnaB by a mechanism akin to that of polymerase clamp loaders and indicate that bacterial replicative helicases, like their eukaryotic counterparts, possess autoregulatory elements that influence how hexameric motor domains are loaded onto and unwind DNA.

Original languageEnglish (US)
Pages (from-to)438-448
Number of pages11
Issue number2
StatePublished - Apr 11 2013
Externally publishedYes

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology


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