Promoters controlling expression of the alternative nitrogenase and the molybdenum uptake system in Rhodobacter capsulatus are activated by NtrC, independent of sigma54, and repressed by molybdenum.
The alternative nitrogenase of Rhodobacter capsulatus is expressed only under conditions of nitrogen and molybdenum depletion. The analysis of anfA-lacZ fusions demonstrated that this dual control occurred at the level of transcription of anfA, which encodes a transcriptional activator specific for the alternative nitrogenase. The anfA promoter was found to be activated under nitrogen-limiting conditions by NtrC in a sigma54-independent manner. In addition, anfA transcription was repressed by traces of molybdenum. This molybdenum-dependent repression of anfA was released in R. capsulatus mutants carrying either lesions in the high-affinity molybdenum uptake system (modABCD) or a double deletion of mopA and mopB, two genes encoding molybdenum-pterin-binding proteins. The expression of the molybdenum transport system itself was shown to be negatively regulated by molybdenum and, unexpectedly, to be also regulated by NtrC. This finding is in line with the presence of two tandemly arranged DNA motifs located in front of the R. capsulatus mopA-modABCD operon, which are homologous to R. capsulatus NtrC binding sites. Mapping of the transcriptional initiation sites of mopA and anfA revealed promoter sequences exhibiting significant homology to each other but no homology to known prokaryotic promoters. In addition, a conserved DNA sequence of dyad symmetry overlapping the transcriptional initiation sites of mopA and anfA was found. Deletions within this element resulted in molybdenum-independent expression of anfA, indicating that this DNA sequence may be the target of MopA/MopB-mediated repression.
Kutsche
M
M
Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Bielefeld, Germany.
Leimkühler
S
S
Angermüller
S
S
Klipp
W
W
D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins; D002874:Chromosome Mapping; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008291:Malate Dehydrogenase / Q000235:genetics; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000378:metabolism*; D009154:Mutation; D009591:Nitrogenase / Q000235:genetics*; D009876:Operon; D051922:PII Nitrogen Regulatory Proteins; D011401:Promoter Regions, Genetic; D051877:RNA Polymerase Sigma 54; D016354:Rhodobacter capsulatus / Q000201:enzymology / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D012808:Sigma Factor / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D026901:Membrane Transport Proteins; D051922:PII Nitrogen Regulatory Proteins; D012808:Sigma Factor; D015534:Trans-Activators; D014157:Transcription Factors; C081166:mopA protein, Rhodobacter capsulatus; C081167:mopB protein, Rhodobacter capsulatus; D008982:Molybdenum; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); D009591:Nitrogenase; D012321:DNA-Directed RNA Polymerases; D051877:RNA Polymerase Sigma 54