Circadian input kinases and their homologs in cyanobacteria: evolutionary constraints versus architectural diversification.
The circadian input kinase A (cikA) gene encodes a protein relaying environmental signal to the central circadian oscillator in cyanobacteria. The CikA protein has a variable architecture and usually consists of four tandemly arrayed domains: GAF, histidine kinase (HisKA), histidine kinase-like ATPase (HATPase_c), and a pseudo-receiver (REC). Among them, HisKA and HATPase_c are the least polymorphic, and REC is not present in heterocystic filamentous cyanobacteria. CikA contains several conserved motifs that are likely important for circadian function. There are at least three types of circadian systems, each of which possesses a different set of circadian genes. The originally described circadian system (kaiABC system) possesses both cikA and kaiA, while the others lack either only cikA (kaiABC (Delta)) or both (kaiBC). The results we obtained allowed us to approximate the time of the cikA origin to be about 2600-2200 MYA and the time of its loss in the species with the kaiABC (Delta) or kaiBC system between 1100 and 600 MYA. Circadian specialization of CikA, as opposed to its non-circadian homologs, is a result of several factors, including the unique conserved domain architecture and high evolutionary constraints of some domains and regions, which were previously identified as critical for the circadian function of the gene.
Baca
Ivan
I
Institute of Genetics, National Academy of Sciences of Moldova, Chisinau, Moldova. bidmd@yahoo.com
Sprockett
Daniel
D
Dvornyk
Volodymyr
V
D000595:Amino Acid Sequence; D000704:Analysis of Variance; D001426:Bacterial Proteins / Q000235:genetics*; D001499:Bayes Theorem; D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics*; D030541:Databases, Genetic; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D017354:Point Mutation; D011494:Protein Kinases / Q000235:genetics*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D011494:Protein Kinases; C411989:CikA protein, bacteria