The symbiotic nitrogen fixation regulatory operon (fixRnifA) ofBradyrhizobium japonicumis expressed aerobically and is subject to a novel,nifA-independent type of activation

Abstract

The Bradyrhizobium japonicum N2 fixation regulatory gene, nifA, was sequenced and its transcription start site determined. Between the start of transcription and the nifA gene an open reading frame of 278 codons was found and named fixR. A deletion in fixR which allowed transcription into nifA resulted in a 50% reduced Fix activity. The fixRnifA operon was expressed in soybean root nodules, in cultures grown anaerobically with nitrate as terminal electron acceptor, in microaerobic cultures, and in aerobic cultures. The transcription start site (+1) was preceded by a characteristic nif(-24/-12)-type promoter consensus sequence. Double base-pair exchanges in the -12 but not in the -24 region resulted in a 'promoter-down' phenotype. A promoter-upstream DNA region between -50 and -148 was essential for maximal promoter activity. Expression from the promoter was not dependent on nifA. We conclude that the fixRnifA promoter is positively controlled, and that it requires a newly postulated transcriptional factor in order to become activated.

The predicted protein product of a pathogenicity locus from Pseudomonas syringae pv. phaseolicola is homologous to a highly conserved domain of several procaryotic regulatory proteins

“…Only minor gaps were required to allow maximum alignment between the three proteins. Comparable levels of similarity were also found between the HrpS product and other NtrC and NifA proteins (16,18,26,28,41) and with the TyrR protein of E. coli (4,14). The above similarities were confined to the central, ca.…”

“…The NtrC protein is the most extensively studied member of this group. In the enteric bacteria (E. coli, S. typhimurium, K. pneumoniae), NtrC operates as part of a global control system (the ntr system) which mediates the transcriptional activation or repression of many different genes and operons (24,32,41). A similar system operates in a variety of species, including Rhizobiulm spp., Bradyrhizobium japonicum, Pseudomonas spp.…”

“…A similar system operates in a variety of species, including Rhizobiulm spp., Bradyrhizobium japonicum, Pseudomonas spp. (41), and Agrobacterium tumefaciens (34). Genes subject to control by the ntr system are involved in a wide variety of catabolic, biosynthetic, transport, and behavioral functions (see reference 41 for references).…”

Cloning and sequencing of the genes involved in the conversion of 5-substituted hydantoins to the corresponding L-amino acids from the native plasmid of Pseudomonas sp. strain NS671

“…The deduced amino acid sequence of ORF1 was found to share strong homology with the gene products of nifA (40 to 46% in 237 to 287 amino acids) from different species (2,6,9,18,21,32), ntrC (42 to 44% in 248 to 264 amino acids) from Klebsiella pneumoniae (6) and E. coli (20), dctD (42% in 231 amino acids) from Rhizobium leguminosarum (24) and Rhizobium meliloti (15), xylR (40% in 229 amino acids) from Pseudomonas putida (13), tyrR (40% in 229 amino acids) from E. coli (7), and hydG (37% in 290 amino acids) from E. coli (29). All of these are regulatory proteins which function at a transcriptional level.…”

Nitrogen fixation genes involved in the Bradyrhizobium japonicum‐soybean symbiosis

“…The aerobic expression from the fixR promoter requires the presence of an upstream activator sequence located around position -66 from the transcription start site. This suggests that under aerobic conditions the fixRnifA operon is controlled positively [23,24].…”