Abstract
Cyanobacteria have developed light-harvesting antenna complex phycobilisome. When cells respond to changes in the a viability of various nutrients or to high light exposure, phycobilisome is rapidly degraded. In the cyanobacterium Synechococcus elongatus PCC 7942, it was suggested that the bleaching process is regulated by two-component histidine kinase NblS. To address the molecular mechanisms of the signaling pathway involving NblS, we carried out the yeast two-hybrid analysis. NblS interacted with the response regulators, RpaB and SrrA. Recombinant NblS had the phosphotransfer activity to RpaB and SrrA, respectively. Gel shift assay revealed that RpaB specifically bound to the upstream region of nblA that was induced by bleaching. In addition, either nblS or rpaB defective mutant exhibited the bleaching phenotypes in normal growth condition and the nblA transcripts accumulated in the mutant. These results suggest that the bleaching process is regulated via NblS-RpaB signaling pathway.
