title: Circadian clock protein KaiC forms ATP-dependent hexameric rings and binds DNA.
abstract: KaiC from Synechococcus elongatus PCC 7942 (KaiC) is an essential circadian clock protein in cyanobacteria. Previous sequence analyses suggested its inclusion in the RecADnaB superfamily. A characteristic of the proteins of this superfamily is that they form homohexameric complexes that bind DNA. We show here that KaiC also forms ring complexes with a central pore that can be visualized by electron microscopy. A combination of analytical ultracentrifugation and chromatographic analyses demonstrates that these complexes are hexameric. The association of KaiC molecules into hexamers depends on the presence of ATP. The KaiC sequence does not include the obvious DNA-binding motifs found in RecA or DnaB. Nevertheless, KaiC binds forked DNA substrates. These data support the inclusion of KaiC into the RecADnaB superfamily and have important implications for enzymatic activity of KaiC in the circadian clock mechanism that regulates global changes in gene expression patterns.
authors.affiliation: Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Mori
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Saveliev
authors.forename: Yao
authors.initials: Y
authors.lastname: Xu
authors.forename: Walter F
authors.initials: WF
authors.lastname: Stafford
authors.forename: Michael M
authors.initials: MM
authors.lastname: Cox
authors.forename: Ross B
authors.initials: RB
authors.lastname: Inman
authors.forename: Carl H
authors.initials: CH
authors.lastname: Johnson
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001683:Biological Clocks; D056925:Circadian Rhythm Signaling Peptides and Proteins; D004247:DNA / Q000378:metabolism*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114271:KaiC protein, cyanobacteria; D000255:Adenosine Triphosphate; D004247:DNA