title: Biochemical analysis of three putative KaiC clock proteins from Synechocystis sp. PCC 6803 suggests their functional divergence.
abstract: Cyanobacteria have been shown to have a circadian clock system that consists mainly of three protein components: KaiA, KaiB and KaiC. This system is well understood in the cyanobacterium Synechococcus elongatus PCC 7942, for which robust circadian oscillations have been shown. Like many other cyanobacteria, the chromosome of the model cyanobacterium Synechocystis sp. PCC 6803 contains additional kaiC and kaiB gene copies besides the standard kaiABC gene cluster. The respective gene products differ significantly in their amino acid sequences, especially in their C-terminal regions, suggesting different functional characteristics. Here, phosphorylation assays of the three Synechocystis sp. PCC 6803 KaiC proteins revealed that KaiC1 phosphorylation depends on KaiA, as is well documented for the Synechococcus elongatus PCC 7942 KaiC protein, whereas KaiC2 and KaiC3 autophosphorylate independently of KaiA. This was confirmed by in vivo protein-protein interaction studies, which demonstrate that only KaiC1 interacts with KaiA. Furthermore, we demonstrate that the three different Kai proteins form only homomeric complexes in vivo. As only KaiC1 phosphorylation depends on KaiA, a prerequisite for robust oscillations, we suggest that the kaiAB1C1 gene cluster in Synechocystis sp. PCC 6803 controls circadian timing in a manner similar to the clock described in Synechococcus elongatus PCC 7942.
authors: Institute for Theoretical Biology, Charité-Universitätsmedizin Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany.
authors: Anika
authors: A
authors: Wiegard
authors: Institute for Microbiology and Molecular Biology, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 26, D-35392 Giessen, Germany.
authors: Anja K
authors: AK
authors: Dörrich
authors: Institute for Microbiology and Molecular Biology, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 26, D-35392 Giessen, Germany.
authors: Hans-Tobias
authors: HT
authors: Deinzer
authors: Institute for Theoretical Biology, Charité-Universitätsmedizin Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany.
authors: Christian
authors: C
authors: Beck
authors: Institute for Microbiology and Molecular Biology, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 26, D-35392 Giessen, Germany.
authors: Annegret
authors: A
authors: Wilde
authors: Institute for Microbiology and Molecular Biology, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 26, D-35392 Giessen, Germany.
authors: Julia
authors: J
authors: Holtzendorff
authors: Institute for Theoretical Biology, Charité-Universitätsmedizin Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany.
authors: Ilka M
authors: IM
authors: Axmann
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D056925:Circadian Rhythm Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D046940:Synechococcus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114269:KaiA protein, cyanobacteria; C114270:KaiB protein, cyanobacteria; C114271:KaiC protein, cyanobacteria