title: Identification and transcriptional analysis of nitrate assimilation genes in the halophilic archaeon Haloferax mediterranei.
abstract: Sequencing a 6,720-bp segment of the extreme halophilic archaeon Haloferax mediterranei genome has revealed the genomic organization of the putative structural genes for nitrate assimilation. We report a gene operon containing nasABC and nasD gene. nasA encodes an assimilatory nitrate reductase, nasB codes for a membrane protein with similarity to the NarK transporter, nasC encodes a protein with similarity to MobA; and nasD codes for an assimilatory ferredoxin-dependent nitrite reductase. Reverse transcription-PCR and primer extension experiments have demonstrated the existence of one polycistronic messenger nasABC and one monocistronic nasD initiated from a different promoter. The gene order and the grouping in two adjacent transcriptional units constitutes a novel organization of nas genes. The promoter regions harbor direct palindromes reminiscent of target sites for binding of a hypotetical regulatory protein(s). Transcription of the nasABC and nasD regions was found to be repressed by the presence of ammonium as nitrogen source.
authors.affiliation: División de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Alicante, Ap. 99, E- 03080, Alicante, Spain.
authors.forename: Belén
authors.initials: B
authors.lastname: Lledó
authors.forename: Frutos C
authors.initials: FC
authors.lastname: Marhuenda-Egea
authors.forename: Rosa María
authors.initials: RM
authors.lastname: Martínez-Espinosa
authors.forename: María José
authors.initials: MJ
authors.lastname: Bonete
mesh_terms: D000595:Amino Acid Sequence; D027321:Anion Transport Proteins / Q000235:genetics; D019843:Archaeal Proteins / Q000235:genetics; D001483:Base Sequence; D019641:DNA, Archaeal / Q000737:chemistry / Q000235:genetics; D050900:Ferredoxin-Nitrite Reductase / Q000235:genetics; D005786:Gene Expression Regulation; D019623:Haloferax mediterranei / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D050901:Nitrate Reductase / Q000235:genetics; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism*; D009876:Operon / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D024363:Transcription Initiation Site
chemical_list: D027321:Anion Transport Proteins; D019843:Archaeal Proteins; D019641:DNA, Archaeal; D000091285:Nitrate Transporters; D009566:Nitrates; D012333:RNA, Messenger; D050900:Ferredoxin-Nitrite Reductase; D050901:Nitrate Reductase