Comprehensive study on transcriptional network system in the photoautotrophic cyanobacteria Synechococcusstrains

点击翻译按钮获取中文摘要

(1) The entire genome of a unicellular cyanobacterium, Synechococcus sp. strain PCC 6301, was sequenced. The genome consisted of a circular chromosome 2,696,255 bp long. A total of 2525 potential protein-encoding genes, two sets of rRNA genes, 45 tRNA genes representing 42 tRNA species and several genes, for small structural RNAs were assigned to the chromosome. Thirty-seven genes for the proteins involved in two-component regulatory system were also annotated. Ten percent of all the protein genes lacked significant similarity to genes for predicted proteins in the public, indicating the genes unique to Synechococcus PCC6301. We constructed high-density DNA microarrays (Affimetrix Gene Chip) of Synechococcus PCC6301 as a tool for comprehensive analysis of transcriptional network in cyanobacteria.(2) We identified three genes responsible for the latent transport activity for nitrate: ltnA, which encodes a response regulator with no effector domain; ltnB, which encodes a hybrid histidine kinase with two receiver domains; and ltnT, which encodes a sulfate permease-like protein with a putative cyclic nucleoside monophosphate (cNMP)-binding domain.(3) Circadian clock of cyanobacteria was considered to be composed of negative feedback regulation of kaiBC expression. We demonstrated that KaiC phosphorylation state oscillated even without kaiBC messenger RNA accumulation under continuous dark conditions. Moreover, kinetic profiles in the ratio of KaiC autophosphorylation-dephosphorylation were also temperature compensated in vitro. Thus, the cyanobacterial clock can keep time independent of de novo transcription and translation processes. Furthermore, we have reconstituted the self-sustainable oscillation of KaiC phosphorylation in vitro. The period of the in vitro oscillation was stable and the circadian periods observed in vivo in KaiC mutant strains were consistent with those measured in vitro.