title: Nitrate assimilation gene cluster from the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120.
abstract: A region of the genome of the filamentous, nitrogen-fixing, heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 that contains a cluster of genes involved in nitrate assimilation has been identified. The genes nir, encoding nitrite reductase, and nrtABC, encoding elements of a nitrate permease, have been cloned. Insertion of a gene cassette into the nir-nrtA region impaired expression of narB, the nitrate reductase structural gene which together with nrtD is found downstream from nrtC in the gene cluster. This indicates that the nir-nrtABCD-narB genes are cotranscribed, thus constituting an operon. Expression of the nir operon in strain PCC 7120 is subjected to ammonium-promoted repression and takes place from an NtcA-activated promoter located 460 bp upstream from the start of the nir gene. In the absence of ammonium, cellular levels of the products of the nir operon are higher in the presence of nitrate than in the absence of combined nitrogen.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Spain.
authors.forename: J E
authors.initials: JE
authors.lastname: Frías
authors.forename: E
authors.initials: E
authors.lastname: Flores
authors.forename: A
authors.initials: A
authors.lastname: Herrero
mesh_terms: D000595:Amino Acid Sequence; D017033:Anabaena / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D015870:Gene Expression; D026901:Membrane Transport Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D016296:Mutagenesis; D009566:Nitrates / Q000378:metabolism*; D009572:Nitrite Reductases / Q000235:genetics*; D010442:Peptide Chain Initiation, Translational; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; D009566:Nitrates; D009572:Nitrite Reductases