title: A KaiC-associating SasA-RpaA two-component regulatory system as a major circadian timing mediator in cyanobacteria.
abstract: KaiA, KaiB, and KaiC clock proteins from cyanobacteria and ATP are sufficient to reconstitute the KaiC phosphorylation rhythm in vitro, whereas almost all gene promoters are under the control of the circadian clock. The mechanism by which the KaiC phosphorylation cycle drives global transcription rhythms is unknown. Here, we report that RpaA, a potential DNA-binding protein that acts as a cognate response regulator of the KaiC-interacting kinase SasA, mediates between KaiC phosphorylation and global transcription rhythms. Circadian transcription was severely attenuated in sasA (Synechococcus adaptive sensor A)- and rpaA (regulator of phycobilisome-associated)-mutant cells, and the phosphotransfer activity from SasA to RpaA changed dramatically depending on the circadian state of a coexisting Kai protein complex in vitro. We propose a model in which the SasA-RpaA two-component system mediates time signals from the enzymatic oscillator to drive genome-wide transcription rhythms in cyanobacteria. Moreover, our results indicate the presence of secondary output pathways from the clock to transcription control, suggesting that multiple pathways ensure a genome-wide circadian system.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Furocho, Nagoya 464-8602, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Takai
authors.forename: Masato
authors.initials: M
authors.lastname: Nakajima
authors.forename: Tokitaka
authors.initials: T
authors.lastname: Oyama
authors.forename: Ryotaku
authors.initials: R
authors.lastname: Kito
authors.forename: Chieko
authors.initials: C
authors.lastname: Sugita
authors.forename: Mamoru
authors.initials: M
authors.lastname: Sugita
authors.forename: Takao
authors.initials: T
authors.lastname: Kondo
authors.forename: Hideo
authors.initials: H
authors.lastname: Iwasaki
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D001683:Biological Clocks; D002940:Circadian Rhythm; D056925:Circadian Rhythm Signaling Peptides and Proteins; D000458:Cyanobacteria / Q000502:physiology*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D008027:Light; D008954:Models, Biological; D009991:Oscillometry; D010766:Phosphorylation; D010770:Phosphotransferases / Q000502:physiology*; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114271:KaiC protein, cyanobacteria; D010770:Phosphotransferases; C083143:SasA protein, Synechococcus