{PDOC51146}
{PS51146; KAIC}
{BEGIN}
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* KaiC domain profile *
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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 [3-5].

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.

-Sequences known to belong to this class detected by the profile: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: September 2005 / First entry.

[ 1] Dvornyk V., Vinogradova O., Nevo E.
     "Origin and evolution of circadian clock genes in prokaryotes."
     Proc. Natl. Acad. Sci. U.S.A. 100:2495-2500(2003).
     PubMed=12604787; DOI=10.1073/pnas.0130099100
[ 2] Dvornyk V., Knudsen B.
     "Functional divergence of the circadian clock proteins in
     prokaryotes."
     Genetica 124:247-254(2005).
     PubMed=16134337
[ 3] Iwasaki H., Taniguchi Y., Ishiura M., Kondo T.
     "Physical interactions among circadian clock proteins KaiA, KaiB and
     KaiC in cyanobacteria."
     EMBO J. 18:1137-1145(1999).
     PubMed=10064581; DOI=10.1093/emboj/18.5.1137
[ 4] Pattanayek R., Wang J., Mori T., Xu Y., Johnson C.H., Egli M.
     "Visualizing a circadian clock protein: crystal structure of KaiC and
     functional insights."
     Mol. Cell 15:375-388(2004).
     PubMed=15304218; DOI=10.1016/j.molcel.2004.07.013
[ 5] Hayashi F., Itoh N., Uzumaki T., Iwase R., Tsuchiya Y., Yamakawa H.,
     Morishita M., Onai K., Itoh S., Ishiura M.
     "Roles of two ATPase-motif-containing domains in cyanobacterial
     circadian clock protein KaiC."
     J. Biol. Chem. 279:52331-52337(2004).
     PubMed=15377674; DOI=10.1074/jbc.M406604200

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