Circadian clock protein KaiC forms ATP-dependent hexameric rings and binds DNA.

Mori T, Saveliev SV, Xu Y, Stafford WF, Cox MM, Inman RB, Johnson CH
Proc Natl Acad Sci U S A. 2002 99 (26): 17203-8

PMID: 12477935 · PMCID: PMC139293 · DOI:10.1073/pnas.262578499

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.

MeSH Terms (8)

Adenosine Triphosphate Amino Acid Sequence Bacterial Proteins Biological Clocks Circadian Rhythm Signaling Peptides and Proteins DNA Microscopy, Electron Molecular Sequence Data

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