Send to

Choose Destination
Mol Gen Genet. 2001 Jan;264(5):623-33.

RpoN of Rhizobium leguminosarum bv. viciae strain VF39SM plays a central role in FnrN-dependent microaerobic regulation of genes involved in nitrogen fixation.

Author information

Department of Biological Sciences, University of Calgary, Alberta, Canada.


The rpoN gene, which codes for the alternative transcription factor sigma54, was cloned and sequenced from Rhizobium leguminosarum strain VF39SM. Construction of a rpoN mutant allowed analysis of the role of RpoN as a transcriptional regulator of genes carrying lacZ reporter fusions. Analysis of a rpoN::lacZ transcriptional fusion in the rpoN background revealed that this gene was negatively autoregulated. Site-directed mutagenesis was used to demonstrate that this autoregulation was dependent on a reverse complement RpoN binding site located upstream of the rpoN gene. rpoN was shown to be required for full microaerobic expression of both copies of fixGHIS, as well as of fixNOQP, despite the absence of apparent rpoN binding sites upstream of fixG. Moreover, rpoN was found to be required for full microaerobic expression of fnrN, which in turn is absolutely required for microaerobic induction of fixGHIS. This suggests that the reduced fixG::lacZ expression seen in the rpoN background is due to the dependence of fnrN expression on RpoN.

[Indexed for MEDLINE]

Supplemental Content

Loading ...
Support Center