title: CalA, a cyanobacterial AbrB protein, interacts with the upstream region of hypC and acts as a repressor of its transcription in the cyanobacterium Nostoc sp. strain PCC 7120.
abstract: The filamentous, heterocystous, nitrogen-fixing cyanobacterium Nostoc sp. strain PCC 7120 may contain, depending on growth conditions, up to two hydrogenases directly involved in hydrogen metabolism. HypC is one out of at least seven auxiliary gene products required for synthesis of a functional hydrogenase, specifically involved in the maturation of the large subunit. In this study we present a protein, CalA (Alr0946 in the genome), belonging to the transcription regulator family AbrB, which in protein-DNA assays was found to interact with the upstream region of hypC. Transcriptional investigations showed that calA is cotranscribed with the downstream gene alr0947, which encodes a putative protease from the abortive infection superfamily, Abi. CalA was shown to interact specifically not only with the upstream region of hypC but also with its own upstream region, acting as a repressor on hypC. The bidirectional hydrogenase activity was significantly downregulated when CalA was overexpressed, demonstrating a correlation with the transcription factor, either direct or indirect. In silico studies showed that homologues to both CalA and Alr0947 are highly conserved proteins within cyanobacteria with very similar physical organizations of the corresponding structural genes. Possible functions of the cotranscribed downstream protein Alr0947 are presented. In addition, we present a three-dimensional (3D) model of the DNA binding domain of CalA and putative DNA binding mechanisms are discussed.
authors.affiliation: Department of Photochemistry and Molecular Science, Angström Laboratories, Uppsala University, Uppsala, Sweden.
authors.forename: Asa
authors.initials: A
authors.lastname: Agervald
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Zhang
authors.forename: Karin
authors.initials: K
authors.lastname: Stensjö
authors.forename: Ellenor
authors.initials: E
authors.lastname: Devine
authors.forename: Peter
authors.initials: P
authors.lastname: Lindblad
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017124:Conserved Sequence / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006859:Hydrogen / Q000378:metabolism; D006864:Hydrogenase / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics; D046937:Nostoc / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; C108874:HypC protein, Bacteria; D012097:Repressor Proteins; D014157:Transcription Factors; D006859:Hydrogen; D006864:Hydrogenase; D010450:Endopeptidases