Absence of the BaeR protein leads to the early initiation of DNA replication in Escherichia coli

Abstract

Escherichia coli cells have dozens of two-component systems to sense and respond to various stimuli, and thereby cope with changing environments. BaeS/BaeR is one such two-component system, and it deals with a variety of envelope stresses. Interestingly, the ArcA/ArcB and TorS/TorR two-component systems are known to be associated with initiation of DNA replication; however, the effects of BaeS/BaeR on initiation of DNA replication remain unknown. Flow cytometry analysis revealed that the average number of replication origins (oriCs) per cell in ΔbaeR mutants was approximately 30% higher than that in wild-type cells. So was the growth rate of ΔbaeR cells. Ectopic expression of BaeR from the pbaeR plasmid reversed the ΔbaeR mutant phenotypes. The results indicate that absence of BaeR leads to the early initiation of DNA replication. Further, deletion of BaeR caused an increase in the amount of DnaA per cell, but did not change concentration of DnaA, which is the initiator protein.The average number of oriCs per cell in Δspy mutants was the same as that found in the wild-type cells although spy gene expression is controlled by BaeR. These results suggest that BaeR may indirectly affect initiation of replication by controlling expression of the dnaA gene.