Related Experiment Video
Updated: Sep 21, 2025

Spectrophotometric Determination of Phycobiliprotein Content in Cyanobacterium Synechocystis
Published on: September 11, 2018
Dual Redox Regulation of the DNA-Binding Activity of the Response Regulator RpaB in the Cyanobacterium Synechocystis
Naoki Kato1, Kazuki Iwata1, Taro Kadowaki1
1Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Saitama, 338-8570 Japan.
Abstract:
The response regulator RpaB plays a central role in transcriptional regulation of photosynthesis-related genes in cyanobacteria. RpaB is phosphorylated by its cognate histidine kinase Hik33 and functions as both an activator and a repressor under low-light conditions, whereas its phosphorylation level and DNA-binding activity promptly decrease upon the upshift of photon flux density, causing changes in the gene expression profile. In this study, we assessed the possibility of redox regulation of the DNA-binding activity of RpaB in Synechocystis sp. PCC 6803 by the addition of inhibitors of photosynthetic electron transport, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, or the reducing agent dithiothreitol under different photon flux densities. Analysis of the phosphorylation level of RpaB revealed that reduction of QA and increase in the availability of reducing equivalents at the acceptor side of photosystem I (PSI) can independently trigger dephosphorylation. The redox-state-dependent regulation by an unidentified thiol other than Cys59 of RpaB is prerequisite for the phosphorylation-dependent regulation of the DNA-binding activity. Environmental signals, recognized by Hik33, and metabolic signals recognized as the availability of reducing equivalents, must be integrated at the master regulator RpaB, in order to attain the flexible regulation of acclimatory responses.
Related Concept Videos
Global Regulatory Systems
Stringent Response in E. coli
Other Stress Responses in Bacteria
Transcriptional Regulation: Riboswitches
Cooperative Binding of Transcription Regulators
Bacterial RNA Polymerase
In most genes, the transcription site is a single base present upstream of the coding sequence. Though RNAP is a catalytically efficient enzyme, it does not recognize...

