Cyanobacterial daily life with Kai-based circadian and diurnal genome-wide transcriptional control in Synechococcus elongatus.

In the unicellular cyanobacterium Synechococcus elongatus PCC 7942, essentially all promoter activities are under the control of the circadian clock under continuous light (LL) conditions. Here, we used high-density oligonucleotide arrays to explore comprehensive profiles of genome-wide Synechococcus gene expression in wild-type, kaiABC-null, and kaiC-overexpressor strains under LL and continuous dark (DD) conditions. In the wild-type strains, >30% of transcripts oscillated significantly in a circadian fashion, peaking at subjective dawn and dusk.

Autonomous synchronization of the circadian KaiC phosphorylation rhythm.

The cyanobacterial circadian oscillator can be reconstituted in vitro by mixing three purified clock proteins, KaiA, KaiB and KaiC, with ATP. The KaiC phosphorylation rhythm persists for at least 10 days without damping. By mixing oscillatory samples that have different phases and analyzing the dynamics of their phase relationships, we found that the robustness of the KaiC phosphorylation rhythm arises from the rapid synchronization of the phosphorylation state and reaction direction (phosphorylation or dephosphorylation) of KaiC proteins.

Translation initiation of cyanobacterial rbcS mRNAs requires the 38-kDa ribosomal protein S1 but not the Shine-Dalgarno sequence: development of a cyanobacterial in vitro translation system.

Little is known about the biochemical mechanism of translation in cyanobacteria though substantial studies have been made on photosynthesis, nitrogen fixation, circadian rhythm, and genome structure. To analyze the mechanism of cyanobacterial translation, we have developed an in vitro translation system from Synechococcus cells using a psbAI-lacZ fusion mRNA as a model template. This in vitro system supports accurate translation from the authentic initiation site of a variety of Synechococcus mRNAs.

Biochemical properties of CikA, an unusual phytochrome-like histidine protein kinase that resets the circadian clock in Synechococcus elongatus PCC 7942.

We recently described the cikA (circadian input kinase A) gene, whose product supplies environmental information to the circadian oscillator in the cyanobacterium Synechococcus elongatus PCC 7942. CikA possesses three distinct domains: a GAF, a histidine protein kinase (HPK), and a receiver domain similar to those of the response regulator family. To determine how CikA functions in providing circadian input, we constructed modified alleles to tag and truncate the protein, allowing analysis of each domain individually.