Site-directed mutagenesis for DnaA

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Re-replication of DNA from a newly replicated origin is normally suppressed so that coupling of DNA replication with cell division proceeds in an orderly manner. However, the molecular mechanisms for suppression remains unknown, even in prokaryotic cells. In my previous research, I demonstrated that the intrinsic ATPase activity of DnaA protein, the initiation factor for ANA replication in Escherichia coli cells, play a major role in the suppression ofre-replication by inactivating the DnaA function. I also found a stimulation factor for the DnaA ATPase activity and showed that the factor was activated only after the initiation of DNA replication. Based on these results, I proposed a new model for the suppression of re-initiation in Escherichia coli cells. In details, we constructed mutant DnaA protein whose ATPase activity is specifically decreased and showed that induction of a mutated DnaA protein caused over-initiation of chromosomal DNA replication in cells, resulting in a dominant lethal phenotype. These observations suggest that the intrinsic ATPase activity of DnaA protein is involved in the suppression of re-initiation from newly replicated origin in cells