PROSITE documentation PDOC51146 [for PROSITE entry PS51146]
KaiC domain profile


The kaiC domain is a ~240 residue domain of the cyanobacterial circadian (daily) clock protein kaiC and related prokaryotic proteins. The domain is named after Synechococcus sp. kaiC, a regulator of the kai genes and circadian oscillations in cyanobacteria ('kai' means cycle in Japanese). The kaiC protein is composed of two kaiC domains. Besides the typical double-domain kaiC, several single-kaiC-domain proteins occur, also in archaea and proteobacteria, and whereof only certain subfamilies perform circadian functions [1,2]. The domain has a recA/dnaB-like sequence and structure (see <PDOC00131>). The kaiC domain includes an ATP/GTP-binding Walker A and B motif (see <PDOC00017>) and a conserved Glu with potential catalytic function. The phosphorylation of kaiC is essential for the rhythmic pattern of gene expression [3,4,5].

The crystal structure of the cyanobacterial kaiC homohexamer shows that the two kaiC domains fold similarly (see <PDB:1U9I>), but differences occur in their ATP binding pockets [4].

Some proteins known to contain a kaiC domain:

  • Cyanobacterial kaiC, a principal circadian clock protein, present in the kaiABC complex. It represses the expression of the kaiBC operon and other global genes.
  • Archaeal UPF0273 protein, a hypothetical protein with a single kaiC domain.

The profile we developed covers the entire kaiC domain.

Last update:

September 2005 / First entry.


Technical section

PROSITE method (with tools and information) covered by this documentation:

KAIC, PS51146; KaiC domain profile  (MATRIX)


1AuthorsDvornyk V. Vinogradova O. Nevo E.
TitleOrigin and evolution of circadian clock genes in prokaryotes.
SourceProc. Natl. Acad. Sci. U.S.A. 100:2495-2500(2003).
PubMed ID12604787

2AuthorsDvornyk V. Knudsen B.
TitleFunctional divergence of the circadian clock proteins in prokaryotes.
SourceGenetica 124:247-254(2005).
PubMed ID16134337

3AuthorsIwasaki H. Taniguchi Y. Ishiura M. Kondo T.
TitlePhysical interactions among circadian clock proteins KaiA, KaiB and KaiC in cyanobacteria.
SourceEMBO J. 18:1137-1145(1999).
PubMed ID10064581

4AuthorsPattanayek R. Wang J. Mori T. Xu Y. Johnson C.H. Egli M.
TitleVisualizing a circadian clock protein: crystal structure of KaiC and functional insights.
SourceMol. Cell 15:375-388(2004).
PubMed ID15304218

5AuthorsHayashi F. Itoh N. Uzumaki T. Iwase R. Tsuchiya Y. Yamakawa H. Morishita M. Onai K. Itoh S. Ishiura M.
TitleRoles of two ATPase-motif-containing domains in cyanobacterial circadian clock protein KaiC.
SourceJ. Biol. Chem. 279:52331-52337(2004).
PubMed ID15377674

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