title: Organization and expression of nitrogen-fixation genes in the aerobic nitrogen-fixing unicellular cyanobacterium Synechococcus sp. strain RF-1.
abstract: Sixteen nif and 'nif-associated' genes (expressed only under conditions of nitrogen fixation) in Synechococcus sp. strain RF-1 have been cloned and sequenced. All of the nif and nif-associated genes identified in Synechococcus RF-1 were arranged in a continuous cluster spanning approximately 18 kb and containing seven operons. The nifH operon (nifH-nifD-nifK) has been reported previously. nifB, fdxN, nifS, nifU and nifP were found to be located upstream of the nifH operon. nifB-fdxN-nifS-nifU were expressed as an operon. A nifP-like gene was found to be located just upstream of nifB. nifE, nifN, nifX, nifW and the nif-associated hesA, hesB and 'fdx' were found to be located downstream from nifK. The genes located downstream from nifK are arranged nifE-nifN-nifX-orf-nifW-hesA-hesB-'+ ++fdx' and span approximately 7 kb. The function of the ORF situated between nifX and nifW is not known. However, it was identified as a counterpart of ORF-2 in Anabaena sp. strain PCC 7120 based on the deduced amino acid sequence. Northern hybridization and primer extension analysis indicated that the nif and nif-associated genes are organized in nifE-nifN, nifX-orf, nifW-hesA-hesB and 'fdx'-containing operons, respectively. According to the results of this study and previous reports, the genes are expressed in a rhythmic pattern with peaks during the dark phase when the culture is grown in a 12 h light/12 h dark regimen. The rhythm persisted after the culture was transferred to continuous illumination.
authors.affiliation: Institute of Botany, Academia Sinica, Nankang, Taipei, Taiwan 115, Republic of China.
authors.forename: Tan-Chi
authors.initials: TC
authors.lastname: Huang
authors.affiliation: Institute of Botany, Academia Sinica, Nankang, Taipei, Taiwan 115, Republic of China.
authors.forename: Rong-Fong
authors.initials: RF
authors.lastname: Lin
authors.affiliation: Institute of Botany, Academia Sinica, Nankang, Taipei, Taiwan 115, Republic of China.
authors.forename: Mu-Kuei
authors.initials: MK
authors.lastname: Chu
authors.affiliation: National Narcotics Bureau, Department of Health, Executive Yuan, Taiwan 115, Republic of China.
authors.forename: Horng-Ming
authors.initials: HM
authors.lastname: Chen
mesh_terms: D000332:Aerobiosis; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002940:Circadian Rhythm / Q000235:genetics*; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000235:genetics*; D005288:Ferredoxins / Q000235:genetics; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics*; D009591:Nitrogenase / Q000235:genetics; D009876:Operon; D010088:Oxidoreductases; D011401:Promoter Regions, Genetic; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D005288:Ferredoxins; C092498:NifB protein, Bacteria; D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase