title: Structure and molecular phylogeny of sasA genes in cyanobacteria: insights into evolution of the prokaryotic circadian system.
abstract: Cyanobacteria are the simplest organisms known to have a circadian system. In addition to the three well-studied kai genes, kaiA, kaiB, and kaiC, an important element of this system is a two-component sensory transduction histidine kinase sasA. Using publicly available data of complete prokaryotic genomes, we performed structural and phylogenetic analyses of the sasA genes. Results show that this gene has a triple-domain structure, and the domains are under different selective constraints. The sasA gene originated in cyanobacteria probably through the fusion of the ancestral kaiB gene with a double-domain, two-component sensory transduction histidine kinase. The results of the phylogenetic analyses suggest that sasA emerged before the kaiA gene, about 3,000-2,500 MYA, and has evolved in parallel with the evolution of the kaiBC cluster. The observed concordant patterns of the sasA and kaiBC evolution suggest that these genes might compose an ancient KaiBC-SasA-based circadian system, without the kaiA gene, and that such a system still exists in some unicellular cyanobacteria.
authors.affiliation: Osteoporosis Research Center and Department of Biomedical Sciences, Creighton University, USA. dvornyk@creighton.edu
authors.forename: Volodymyr
authors.initials: V
authors.lastname: Dvornyk
authors.forename: Hong-Wen
authors.initials: HW
authors.lastname: Deng
authors.forename: Eviatar
authors.initials: E
authors.lastname: Nevo
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D002940:Circadian Rhythm / Q000235:genetics*; D019295:Computational Biology; D000458:Cyanobacteria / Q000235:genetics*; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D008969:Molecular Sequence Data; D010770:Phosphotransferases / Q000235:genetics*; D010802:Phylogeny; D011401:Promoter Regions, Genetic; D046940:Synechococcus / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D010770:Phosphotransferases; C083143:SasA protein, Synechococcus