title: The AbrB2 autorepressor, expressed from an atypical promoter, represses the hydrogenase operon to regulate hydrogen production in Synechocystis strain PCC6803.
abstract: We have thoroughly investigated the abrB2 gene (sll0822) encoding an AbrB-like regulator in the wild-type strain of the model cyanobacterium Synechocystis strain PCC6803. We report that abrB2 is expressed from an active but atypical promoter that possesses an extended -10 element (TGTAATAT) that compensates for the absence of a -35 box. Strengthening the biological significance of these data, we found that the occurrence of an extended -10 promoter box and the absence of a -35 element are two well-conserved features in abrB2 genes from other cyanobacteria. We also show that AbrB2 is an autorepressor that is dispensable to cell growth under standard laboratory conditions. Furthermore, we demonstrate that AbrB2 also represses the hox operon, which encodes the Ni-Fe hydrogenase of biotechnological interest, and that the hox operon is weakly expressed even though it possesses the two sequences resembling canonical -10 and -35 promoter boxes. In both the AbrB2-repressed promoters of the abrB2 gene and the hox operon, we found a repeated DNA motif [TT-(N(5))-AAC], which could be involved in AbrB2 repression. Supporting this hypothesis, we found that a TT-to-GG mutation of one of these elements increased the activity of the abrB2 promoter. We think that our abrB2-deleted mutant with increased expression of the hox operon and hydrogenase activity, together with the reporter plasmids we constructed to analyze the abrB2 gene and the hox operon, will serve as useful tools to decipher the function and the regulation of hydrogen production in Synechocystis.
authors.affiliation: UMR8221, CEA, CNRS, Université Paris Sud, iBiTec-S, LBBC, Gif sur Yvette, France.
authors.forename: Jérémy
authors.initials: J
authors.lastname: Dutheil
authors.forename: Panatda
authors.initials: P
authors.lastname: Saenkham
authors.forename: Samer
authors.initials: S
authors.lastname: Sakr
authors.forename: Christophe
authors.initials: C
authors.lastname: Leplat
authors.forename: Marcia
authors.initials: M
authors.lastname: Ortega-Ramos
authors.forename: Hervé
authors.initials: H
authors.lastname: Bottin
authors.forename: Laurent
authors.initials: L
authors.lastname: Cournac
authors.forename: Corinne
authors.initials: C
authors.lastname: Cassier-Chauvat
authors.forename: Franck
authors.initials: F
authors.lastname: Chauvat
mesh_terms: D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D033141:Genetic Determinism; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon / Q000502:physiology*; D011401:Promoter Regions, Genetic; D046939:Synechocystis / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D018076:DNA, Complementary; D006859:Hydrogen; D006864:Hydrogenase