Rapid turnover of DnaA at replication origin regions contributes to initiation control of DNA replication

PLoS Genet. 2017 Feb 6;13(2):e1006561. doi: 10.1371/journal.pgen.1006561. eCollection 2017 Feb.

Abstract

DnaA is a conserved key regulator of replication initiation in bacteria, and is homologous to ORC proteins in archaea and in eukaryotic cells. The ATPase binds to several high affinity binding sites at the origin region and upon an unknown molecular trigger, spreads to several adjacent sites, inducing the formation of a helical super structure leading to initiation of replication. Using FRAP analysis of a functional YFP-DnaA allele in Bacillus subtilis, we show that DnaA is bound to oriC with a half-time of 2.5 seconds. DnaA shows similarly high turnover at the replication machinery, where DnaA is bound to DNA polymerase via YabA. The absence of YabA increases the half time binding of DnaA at oriC, showing that YabA plays a dual role in the regulation of DnaA, as a tether at the replication forks, and as a chaser at origin regions. Likewise, a deletion of soj (encoding a ParA protein) leads to an increase in residence time and to overinitiation, while a mutation in DnaA that leads to lowered initiation frequency, due to a reduced ATPase activity, shows a decreased residence time on binding sites. Finally, our single molecule tracking experiments show that DnaA rapidly moves between chromosomal binding sites, and does not arrest for more than few hundreds of milliseconds. In Escherichia coli, DnaA also shows low residence times in the range of 200 ms and oscillates between spatially opposite chromosome regions in a time frame of one to two seconds, independently of ongoing transcription. Thus, DnaA shows extremely rapid binding turnover on the chromosome including oriC regions in two bacterial species, which is influenced by Soj and YabA proteins in B. subtilis, and is crucial for balanced initiation control, likely preventing fatal premature multimerization and strand opening of DnaA at oriC.

MeSH terms

  • Adenosine Triphosphatases / genetics
  • Bacillus subtilis / genetics
  • Bacterial Proteins / genetics*
  • DNA Replication / genetics*
  • DNA-Binding Proteins / genetics*
  • Escherichia coli / genetics
  • Gene Expression Regulation, Bacterial
  • Mutation
  • Origin Recognition Complex / genetics*
  • Replication Origin / genetics

Substances

  • Bacterial Proteins
  • DNA-Binding Proteins
  • DnaA protein, Bacteria
  • OriC chromosomal replication origin
  • Origin Recognition Complex
  • Adenosine Triphosphatases

Grants and funding

We thank Nina el Najjar, University of Marburg, for kindly generating the B. subtilis strain expressing spo0J-yfp for our study. This work was supported by the Deutsche Forschungsgemeinschaft, the Alexander von Humboldt Foundation, and the LOEWE Program of the State of Hessen, for the Centre of Synthetic Microbiology, SYNMIKRO, in Marburg. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.