title: Co-regulation of the nitrogen-assimilatory gene cluster in Clostridium saccharobutylicum.
abstract: Nitrogen assimilation is important during solvent production by Clostridium saccharobutylicum NCP262, as acetone and butanol yields are significantly affected by the nitrogen source supplied. Growth of this bacterium was dependent on the concentration of organic nitrogen supplied and the expression of the assimilatory enzymes, glutamine synthetase (GS) and glutamate synthase (GOGAT), was shown to be induced in nitrogen-limiting conditions. The regions flanking the gene encoding GS, glnA, were isolated from C. saccharobutylicum genomic DNA, and DNA sequencing revealed that the structural genes encoding the GS (glnA) and GOGAT (gltA and gltB) enzymes were clustered together with the nitR gene in the order glnA-nitR-gltAB. RNA analysis showed that the glnA-nitR and the gltAB genes were co-transcribed on 2.3 and 6.2 kb RNA transcripts respectively, and that all four genes were induced under the same nitrogen-limiting conditions. Complementation of an Escherichia coli gltD mutant, lacking a GOGAT small subunit, was achieved only when both the C. saccharobutylicum gltA and gltB genes were expressed together under anaerobic conditions. This is believed to be the first functional analysis of a gene cluster encoding the key enzymes of nitrogen assimilation, GS and GOGAT. A similar gene arrangement is seen in Clostridium beijerinckii NCIMB 8052, and based on the common regulatory features of the promoter regions upstream of the glnA operons in both species, we suggest a model for their co-ordinated regulation by an antitermination mechanism as well as antisense RNA.
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7701, South Africa.
authors.forename: Helen E
authors.initials: HE
authors.lastname: Stutz
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7701, South Africa.
authors.forename: Keith W M
authors.initials: KWM
authors.lastname: Quixley
authors.affiliation: Department of Food and Agricultural Sciences, Cape Technikon, Cape Town 8001, South Africa.
authors.forename: Lynn D
authors.initials: LD
authors.lastname: McMaster
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7701, South Africa.
authors.forename: Sharon J
authors.initials: SJ
authors.lastname: Reid
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D003013:Clostridium / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005970:Glutamate Synthase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009584:Nitrogen / Q000378:metabolism* / Q000494:pharmacology; D016372:RNA, Antisense / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D016372:RNA, Antisense; D016601:RNA-Binding Proteins; C064872:antiterminator proteins, Bacteria; D005970:Glutamate Synthase; C081173:glutamine synthetase I; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen