Characterization of a fixLJ-regulated Bradyrhizobium japonicum gene sharing similarity with the Escherichia coli fnr and Rhizobium meliloti fixK genes

Anthamatten, Denise; Scherb, B; Hennecke, Hauke

doi:10.1128/jb.174.7.2111-2120.1992

Cited by 79 publications

(69 citation statements)

References 58 publications

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“…Furthermore, three genes encoding small, homologous Hsps have recently been described (hspA, hspB, and hspC ; Narberhaus et al, 1996). Other genes are duplicated, as was reported for nodD (Gö ttfert et al, 1992), fixK (Anthamatten et al, 1992;Fischer, 1994), and for another sigma factor, namely 54 (Kullik et al, 1991 (Landick et al, 1984); Citrobacter freundii, Serratia marcescens, Agrobacterium tumefaciens, and Zymomonas mobilis (Nakahigashi et al, 1995); Haemophilus influenzae (Fleischmann et al, 1995); Vibrio cholerae (J. Das, unpublished; Accession No. U44432); Pseudomonas aeruginosa (Benvenisti et al, 1995;Naczynski et al, 1995); Caulobacter crescentus (Reisenauer et al, 1996;Wu and Newton, 1996); Myxococcus xanthus RpoC (Apelian and Inouye, 1993).…”

Section: Discussionmentioning

confidence: 99%

Three disparately regulated genes for σ³²‐like transcription factors in Bradyrhizobium japonicum

Narberhaus

Krummenacher

Fischer

et al. 1997

Molecular Microbiology

119

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Section: Discussionmentioning

confidence: 99%

Three disparately regulated genes for σ³²‐like transcription factors in Bradyrhizobium japonicum

Narberhaus

Krummenacher

Fischer

et al. 1997

Molecular Microbiology

119

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“…Despite being homologous to nitrogen fixation regulatory proteins in other bacteria, strains with mutations in this gene are still Nif ϩ (1). Nevertheless, Anthamatten et al (1) have suggested that this protein is involved in the regulation of other oxygen-responsive systems, such as hydrogenase.…”

Section: Discussionmentioning

confidence: 99%

Roles of HoxX and HoxA in biosynthesis of hydrogenase in Bradyrhizobium japonicum

Durmowicz

Maier

1997

J Bacteriol

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In-frame deletion mutagenesis was used to study the roles of two Bradyrhizobium japonicum proteins, HoxX and HoxA, in hydrogenase biosynthesis; based on their sequences, these proteins were previously proposed to be sensor and regulator proteins, respectively, of a two-component regulatory system necessary for hydrogenase transcription. Deletion of the hoxX gene resulted in a strain that expressed only 30 to 40% of wild-type hydrogenase activity. The inactive unprocessed form of the hydrogenase large subunit accumulated in this strain, indicating a role for HoxX in posttranslational processing of the hydrogenase enzyme but not in transcriptional regulation. Strains containing a deletion of the hoxA gene or a double mutation (hoxX and hoxA) did not exhibit any hydrogenase activity under free-living conditions, and extracts from these strains were inactive in gel retardation assays with a 158-bp fragment of the DNA region upstream of the hupSL operon. However, bacteroids from root nodules formed by all three mutant types (hoxX, hoxA, and hoxX hoxA) exhibited hydrogenase activity comparable to that of wild-type bacteroids. Bacteroid extracts from all of these strains, including the wild type, failed to cause a shift of the hydrogenase upstream region used in our assay. It was shown that HoxA is a DNA-binding transcriptional activator of hydrogenase structural gene expression under free-living conditions but not under symbiotic conditions. Although symbiotic hydrogenase expression is still 54 dependent, a transcriptional activator other than HoxA functions presumably upstream of the HoxA binding site.Bradyrhizobium japonicum, the slow-growing, nitrogen-fixing symbiont of the soybean plant, expresses a hydrogen uptake hydrogenase that oxidizes hydrogen into its constituent protons and electrons. During symbiosis, the nickel-containing hydrogenase is thought to help improve the efficiency of nitrogen fixation in root nodules by passing H 2 -derived electrons to the electron transport chain, thereby recycling energy lost during nitrogen fixation (21). In B. japonicum, hydrogenase activity can also be induced under free-living, microaerobic conditions. Most studies of hydrogenase expression in this organism have been done under these conditions (21).Studies of the regulation of hydrogenase expression have shown that the hydrogenase structural genes, hupS and hupL, are regulated at the transcriptional level by hydrogen, oxygen, and nickel (14). Subsequently, a 50-bp region from base Ϫ99 to base Ϫ149 upstream of the transcriptional start site that is necessary for this regulation was identified (16). In addition, the hydrogenase promoter is 54 dependent and also uses integration host factor for full induction (4). Because the same cis-acting genetic region is responsible for regulation by the three environmental components, it is thought that the three signals are somehow integrated and passed on to a single activating factor that then binds within the 50-bp regulatory region to affect transcription (15).Previous sequenci...

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“…The cultures were incubated, with the flasks shaken and the test tubes on a rotary wheel. Similar protocols have been used to study oxygen effects on expression of other B. japonicum genes (3,31). For the time course experiment whose results are shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…In nodules, this oxygen control is likely to occur via the same two-step regulatory cascade already shown to control nif and fix genes in various rhizobial species. These oxygen-regulated genes are activated via the FixLJ two-component regulatory system (1,3,10,25). FixL (17,34), the sensor, is a hemoprotein that under low-oxygen conditions transmits a signal via phosphorylation to the response regulator, FixJ (20,41), which in turn activates specific nif and fix genes (30,45,59,60).…”

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confidence: 99%

“…Fnr controls the expression of target genes in response to anoxia by binding to a specific promoter motif termed an Fnr box (for reviews, see reference 21, 54, and 55). Rhizobial Fnr-like proteins include FixK from Rhizobium meliloti (7), FixK 1 and FixK 2 from B. japonicum (2,3), and FnrN from Rhizobium leguminosarum biovar viciae (8). As might be expected, Fnr boxes have been noted upstream of a number of rhizobial genes, including the B. japonicum hemA gene (15,38,40,44).…”

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confidence: 99%

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Oxygen control of the Bradyrhizobium japonicum hemA gene

Page

Guerinot

1995

J Bacteriol

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The hemA gene of Bradyrhizobium japonicum, which encodes the first enzyme in the heme biosynthetic pathway, is regulated by oxygen. Up to ninefold induction of ␤-galactosidase activity is seen when cultures of B. japonicum containing either a plasmid-encoded or a chromosomally integrated hemA-lacZ fusion are shifted to restricted aeration. The oxygen effect is mediated via the FixLJ two-component regulatory system, which regulates the expression of a number of genes involved in the nitrogen fixation process in response to low-oxygen conditions; oxygen induction is lost when the hemA-lacZ fusion is expressed in strains of B. japonicum carrying mutations in fixL or fixJ. The B. japonicum hemA promoter region contains a sequence identical to the Escherichia coli Fnr binding site (positions ؊46 to ؊33 relative to the hemA transcription start site). Fnr is a regulatory protein necessary for the oxygen-regulated expression of anaerobic respiratory genes. Activity of a hemA-lacZ fusion construct in which the Fnr box-like sequence was replaced with a BglII site is not induced in B. japonicum cultures grown under restricted aeration. The fnr homolog fixK is FixLJ dependent. Collectively, these data suggest a role for the rhizobial Fnr-like protein, FixK, in the regulation of hemA. Furthermore, the coregulation of hemA with symbiotically important genes via FixLJ is consistent with the idea that hemA is required in the nodule as well as under free-living conditions.Bradyrhizobium japonicum can live free in the soil or it can enter into a symbiotic relationship with soybean plants that results in the development of nodules, specialized structures on the plant's roots within which the bacteria reside and fix nitrogen. One prominent feature of these nodules is that they are microaerobic (23), which raises the question of how the symbiotic bacteria, called bacteroids, can operate at very low oxygen levels while meeting the high-energy demands of nitrogen fixation. Adaptations by both the plant and the bacterial partners provide the solution to this seeming dilemma, as these adaptations allow efficient bacteroid respiration to take place in nodules. Briefly, bacteroids utilize a terminal oxidase complex different from that used by free-living cells (4

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Characterization of a fixLJ-regulated Bradyrhizobium japonicum gene sharing similarity with the Escherichia coli fnr and Rhizobium meliloti fixK genes

Cited by 79 publications

References 58 publications

Three disparately regulated genes for σ³²‐like transcription factors in Bradyrhizobium japonicum

Three disparately regulated genes for σ³²‐like transcription factors in Bradyrhizobium japonicum

Roles of HoxX and HoxA in biosynthesis of hydrogenase in Bradyrhizobium japonicum

Oxygen control of the Bradyrhizobium japonicum hemA gene

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Characterization of a fixLJ-regulated Bradyrhizobium japonicum gene sharing similarity with the Escherichia coli fnr and Rhizobium meliloti fixK genes

Cited by 79 publications

References 58 publications

Three disparately regulated genes for σ32‐like transcription factors in Bradyrhizobium japonicum

Three disparately regulated genes for σ32‐like transcription factors in Bradyrhizobium japonicum

Roles of HoxX and HoxA in biosynthesis of hydrogenase in Bradyrhizobium japonicum

Oxygen control of the Bradyrhizobium japonicum hemA gene

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Three disparately regulated genes for σ³²‐like transcription factors in Bradyrhizobium japonicum

Three disparately regulated genes for σ³²‐like transcription factors in Bradyrhizobium japonicum