Abstract
Circadian rhythms, endogenous oscillations of physiological activities with a period of ~24 h, are found in a wide spectrum of organisms and enhance their fitness in a day/night alternating environment. Cyanobacteria are the simplest organisms that exhibit circadian rhythms. In cyanobacterium Synechococcus elongatus PCC 7942, KaiC is an essential protein for circadian rhythm generation. We screened KaiC-association protein and isolated DnaA, which is known as DNA replication initiation factor in bacteria. Disruption of dnaA gene in wild-type cell shortened the period of gene expression in Synechococcus elongatus PCC 7942, and mutants with inactivated dnaA were viable. DnaA and KaiC formed complex especially at night and DNA binding domain of DnaA was important for DnaA function. The dnaA-null mutant differently responded to light/dark signal from wild type. Thus, we proposed that DnaA is a modifier of circadian rhythm by participating in light entrainment pathway.
