CTXφ Replication Depends on the Histone-Like HU Protein and the UvrD Helicase

PLoS Genet. 2015 May 20;11(5):e1005256. doi: 10.1371/journal.pgen.1005256. eCollection 2015 May.


The Vibrio cholerae bacterium is the agent of cholera. The capacity to produce the cholera toxin, which is responsible for the deadly diarrhea associated with cholera epidemics, is encoded in the genome of a filamentous phage, CTXφ. Rolling-circle replication (RCR) is central to the life cycle of CTXφ because amplification of the phage genome permits its efficient integration into the genome and its packaging into new viral particles. A single phage-encoded HUH endonuclease initiates RCR of the proto-typical filamentous phages of enterobacteriaceae by introducing a nick at a specific position of the double stranded DNA form of the phage genome. The rest of the process is driven by host factors that are either essential or crucial for the replication of the host genome, such as the Rep SF1 helicase. In contrast, we show here that the histone-like HU protein of V. cholerae is necessary for the introduction of a nick by the HUH endonuclease of CTXφ. We further show that CTXφ RCR depends on a SF1 helicase normally implicated in DNA repair, UvrD, rather than Rep. In addition to CTXφ, we show that VGJφ, a representative member of a second family of vibrio integrative filamentous phages, requires UvrD and HU for RCR while TLCφ, a satellite phage, depends on Rep and is independent from HU.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • DNA Helicases / genetics
  • DNA Helicases / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Gene Deletion
  • Genome, Viral
  • Inovirus / genetics*
  • Inovirus / physiology
  • Vibrio cholerae / enzymology
  • Vibrio cholerae / virology
  • Virus Replication*


  • Bacterial Proteins
  • DNA-Binding Proteins
  • histone-like protein HU, bacteria
  • DNA Helicases

Grant support

This work was supported by a grant from the Agence Nationale pour la Recherche [ANR-11-BLAN-O2401; www.agence-nationale-recherche.fr/] and from the Fondation Bettencourt Schueller [2012 Coup d'Elan award; http://www.fondationbs.org/]. The lab is also supported by the European Research Council under the European Community’s Seventh Framework Programme [FP7/2007-2013 Starting Grant Agreement no. 281590; http://erc.europa.eu/]. The funders played no role in our study.