title: Regulation of V-nitrogenase genes in Anabaena variabilis by RNA processing and by dual repressors.
abstract: Anabaena variabilis ATCC 29413 fixes nitrogen in specialized cells called heterocysts using either a Mo-nitrogenase or a V-nitrogenase. V-nitrogenase structural genes, vnfDGK, as well as vnfEN form an operon with ava4025, located upstream of vnfDG that is repressed by fixed nitrogen and by Mo. The ava4025-vnfDGKEN operon is under the control of a Mo-repressible promoter located nearly 600 bp upstream of ava4025. Levels of vnfDG transcript were about 500-fold higher than ava4025, the first gene of the operon. This may be the result of RNA processing at a site 87 bp upstream of vnfDG that was initially identified as the transcription start site. A strain with a deletion in the coding region of ava4025 grew diazotrophically with Mo or with V. Two similar proteins, VnfR1 and VnfR2, whose genes are located some distance from the ava4025-vnfDGKEN operon, each repressed transcription from the ava4025-vnfDGKEN promoter and a mutant lacking both VnfR1 and VnfR2 made the V-nitrogenase in the presence of Mo. Overexpression of the V-nitrogenase in the double vnfR1 vnfR2 mutant resulted in decreased activity of the Mo-nitrogenase. VnfR1 bound specifically, in vitro, to a region upstream of the ava4025 promoter.
authors.affiliation: University of Missouri - St. Louis, Dept. of Biology, Research 223, St. Louis, MO 63121, USA.
authors.forename: Brenda S
authors.initials: BS
authors.lastname: Pratte
authors.forename: Ryan
authors.initials: R
authors.lastname: Sheridan
authors.forename: Jessie A
authors.initials: JA
authors.lastname: James
authors.forename: Teresa
authors.initials: T
authors.lastname: Thiel
mesh_terms: D046870:Anabaena variabilis / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000494:pharmacology; D009154:Mutation; D009584:Nitrogen / Q000494:pharmacology; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000235:genetics / Q000378:metabolism*; D009876:Operon; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000378:metabolism*; D014158:Transcription, Genetic; D014639:Vanadium / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D012329:RNA, Bacterial; D014639:Vanadium; D008982:Molybdenum; D009591:Nitrogenase; D009584:Nitrogen