ChlH, the H subunit of the Mg-chelatase, is an anti-sigma factor for SigE in Synechocystis sp. PCC 6803

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 16; pp. 6860 - 6865
• Main Authors: Osanai, Takashi, Imashimizu, Masahiko, Seki, Asako, Sato, Shusei, Tabata, Satoshi, Imamura, Sousuke, Asayama, Munehiko, Ikeuchi, Masahiko, Tanaka, Kan
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 21.04.2009; National Acad Sciences
• Subjects: Antiserum; Bacteria; Bacterial Proteins - metabolism; Biological Sciences; Complex Systems: From Chemistry to Systems Biology Special Feature; Cyanobacteria; DNA-Directed RNA Polymerases - metabolism; Enzymes; Gene expression regulation; Genes; Immunoblotting; Immunoprecipitation; Light; Lyases - metabolism; Magnesium; Magnesium - pharmacology; Models, Biological; Mutation - genetics; Plastids; Protein Binding - drug effects; Protein Binding - radiation effects; Protein Subunits - metabolism; Recombinant Fusion Proteins - metabolism; Repressor Proteins - metabolism; Resins; RNA; Sigma Factor - metabolism; Studies; Synechocystis; Synechocystis - drug effects; Synechocystis - enzymology; Synechocystis - radiation effects; Transcription, Genetic - drug effects; Transcription, Genetic - radiation effects; Transitions; Yeasts
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0810040106

Although regulation of sigma factors has been intensively investigated, anti-sigma factors have not been identified in oxygenic photosynthetic organisms. A previous study suggested that the sigma factor, SigE, of the cyanobacterium Synechocystis sp. PCC 6803, a positive regulator of sugar catabolism, is posttranslationally activated by light-to-dark transition. In the present study, we found that the H subunit of Mg-chelatase ChlH interacts with sigma factor SigE by yeast two-hybrid screening, and immunoprecipitation analysis revealed that ChlH associates with SigE in a light-dependent manner in vivo. We also found that Mg²⁺ promotes the interaction of SigE and ChlH and determines their localization in vitro. In vitro transcription analysis demonstrated that ChlH inhibits the transcription activity of SigE. Based on these results, we propose a model in which ChlH functions as an anti-sigma factor, transducing light signals to SigE in a process mediated by Mg²⁺.