The Rhizobium leguminosarum FnrN protein is functionally similar to Escherichia coli Fnr and promotes heterologous oxygen-dependent activation of transcription.
An open reading frame from Rhizobium leguminosarum bv. viciae strain VF39, previously identified and found to be similar to Escherichia coli fnr and Rhizobium meliloti fixK (orf240, thereafter called fnrN), was further analysed. Analysis of the expression of an fnrN-lacZ transcriptional fusion revealed that fnrN is preferentially expressed under oxygen limitation. Using R. meliloti fixN-lacZ fusions it was shown that the fnrN gene product only mediates transcriptional activation under microaerobiosis, indicating that the FnrN protein responds, directly or indirectly, to oxygen. Plasmids which expressed fnrN under the control of an E. coli promoter were able to complement an E. coli fnr mutant with respect to anaerobic growth on nitrate but not fumarate, and to promote anaerobic but not aerobic activation of the Fnr-dependent E. coli genes narGHJI, nirB and fdnGHI coding for nitrate reductase, NADH-dependent nitrite reductase and formate dehydrogenase-N, respectively. Fumarate and DMSO reductase activities were not induced by FnrN. The E. coli fnr gene substituted for fnrN in oxygen-regulated transcription of nirB- and fixN-lacZ fusions in R. leguminosarum. The results indicate that Fnr and FnrN are functionally very similar and share a common mode of oxygen-dependent transcriptional activation. From hybridization studies, it appeared that fnrN-like genes are present in a number of different R. leguminosarum strains.
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Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Germany.
Patschkowski
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Unden
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Priefer
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UB
D000595:Amino Acid Sequence; D000693:Anaerobiosis / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D004790:Enzyme Induction; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D007506:Iron-Sulfur Proteins; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010100:Oxygen / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D016961:Rhizobium leguminosarum / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity; D013385:Succinate Dehydrogenase / Q000096:biosynthesis / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D007506:Iron-Sulfur Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D013385:Succinate Dehydrogenase; D010100:Oxygen