Escherichia coli Dps interacts with DnaA protein to impede initiation: a model of adaptive mutation.
During exponential growth, the level of Dps transiently increases in response to oxidative stress to sequester and oxidize Fe2+, which would otherwise lead to hydroxyl radicals that damage the bacterial chromosome. We report that Dps specifically interacts with DnaA protein by affinity chromatography and a solid phase binding assay, requiring the N-terminal region of DnaA to interact. In vitro, Dps inhibits DnaA function in initiation by interfering with strand opening of the replication origin. Comparing isogenic dps+ and dps::kan strains by flow cytometry and by quantitative polymerase chain reaction assays at either the chromosomally encoded level, or at an elevated level encoded by an inducible plasmid, we show that Dps causes less frequent initiations. Results from genetic experiments support this conclusion. We suggest that Dps acts as a checkpoint during oxidative stress to reduce initiations, providing an opportunity for mechanisms to repair oxidative DNA damage. Because Dps does not block initiations absolutely, duplication of the damaged DNA is expected to increase the genetic variation of a population, and the probability that genetic adaptation leads to survival under conditions of oxidative stress.
Chodavarapu
Sundari
S
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824-1319, USA.
Gomez
Ruben
R
Vicente
Matias
M
Kaguni
Jon M
JM
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D004261:DNA Replication / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D008274:Magnesium / Q000494:pharmacology; D009154:Mutation; D011485:Protein Binding / Q000187:drug effects; D018741:Replication Origin / Q000235:genetics; D014158:Transcription, Genetic
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C066312:DnaA protein, Bacteria; D029968:Escherichia coli Proteins; C088010:dps protein, E coli; D008274:Magnesium