The arc two-component signal transduction system inhibits in vitro Escherichia coli chromosomal initiation

Under anaerobic growth conditions, Escherichia coil operates a two-componen t signal transduction system, termed Are, that consists of ArcB protein, a transmembrane sensor kinase and ArcA protein, the cognate response regulato r. In response to low oxygen levels, autophosphorylated ArcB phosphorylates ArcA, and the resulting phosphorylated ArcA (ArcA-P) functions as a transc riptional regulator of the genes necessary to maintain anaerobic growth. Un der anaerobic conditions, cells maintain a slow growth rate, suggesting tha t the initiation of chromosomal replication is regulated to reduce the init iation frequency. DNase I footprinting experiments revealed that ArcA-P bin ds to the left region of the chromosomal origin, oriC, ArcA-P did not affec t the in vitro replication of plasmid DNA containing the ColE1 origin nor t he in vitro replication of viral DNAs; however, ArcA-P specifically inhibit ed in vitro E, coil chromosomal replication. This inhibition was caused by the prevention of open complex formation, a necessary step in the initiatio n of chromosomal replication. Our in vitro results suggest that the Are two -component system participates in regulating chromosomal initiation under a naerobic growth conditions.