DnaC Inactivation in Escherichia coli K-12 Induces the SOS Response and Expression of Nucleotide Biosynthesis Genes

Department of Science, Systems and Models, Roskilde University, Roskilde, Denmark.
PLoS ONE (Impact Factor: 3.23). 02/2008; 3(8):e2984. DOI: 10.1371/journal.pone.0002984
Source: PubMed


Initiation of chromosome replication in E. coli requires the DnaA and DnaC proteins and conditionally-lethal dnaA and dnaC mutants are often used to synchronize cell populations.
DNA microarrays were used to measure mRNA steady-state levels in initiation-deficient dnaA46 and dnaC2 bacteria at permissive and non-permissive temperatures and their expression profiles were compared to MG1655 wildtype cells. For both mutants there was altered expression of genes involved in nucleotide biosynthesis at the non-permissive temperature. Transcription of the dnaA and dnaC genes was increased at the non-permissive temperature in the respective mutant strains indicating auto-regulation of both genes. Induction of the SOS regulon was observed in dnaC2 cells at 38 degrees C and 42 degrees C. Flow cytometric analysis revealed that dnaC2 mutant cells at non-permissive temperature had completed the early stages of chromosome replication initiation.
We suggest that in dnaC2 cells the SOS response is triggered by persistent open-complex formation at oriC and/or by arrested forks that require DnaC for replication restart.

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    • "We may also exclude the possibility that a ΔsfiA mutation – which we introduced in priA2 cells to prevent the priA2-induced SOS response to inhibit cell division – modulate the stability of RF or the rate at which they are inactivated since we established that the rate, at which inactivated RF accumulate, was identical in dnaC2 sfiA+ and in dnaC2 sfiA− cells (data not shown). An additional point may be made with regards to the SOS response: is it possible that the SOS response, which is induced in dnaC2 cells at non-permissive temperature [23], modifies the fate of ongoing rounds of replication? In this respect, an over-stabilization of active RF in dnaC2 cells in response to the induction of the SOS response may be excluded since this response is induced in priA2 cells as well. "
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