title: ChlH, the H subunit of the Mg-chelatase, is an anti-sigma factor for SigE in Synechocystis sp. PCC 6803.
abstract: 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 Mg(2+) 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 Mg(2+).
authors.affiliation: Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan. cosanai@mail.ecc.u-tokyo.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Osanai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Imashimizu
authors.forename: Asako
authors.initials: A
authors.lastname: Seki
authors.forename: Shusei
authors.initials: S
authors.lastname: Sato
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Sousuke
authors.initials: S
authors.lastname: Imamura
authors.forename: Munehiko
authors.initials: M
authors.lastname: Asayama
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ikeuchi
authors.forename: Kan
authors.initials: K
authors.lastname: Tanaka