Site-directed mutagenesis of NnrR:: a transcriptional regulator of nitrite and nitric oxide reductase in Rhodobacter sphaeroides

NnrR, a transcriptional activator and member of the CRP/FNR family of regulators, is responsible for controlling the expression of a number of denitrification genes in Rhodobacter sphaeroides 2.4.3. The apparent effector for NnrR is nitric oxide, and in its presence NnrR activates expression of the nirK gene and the nor operon, encoding nitrite reductase and nitric oxide reductase, respectively. Whether nitric oxide directly interacts with NnrR to activate transcription is unknown. Other denitrifiers carry putative orthologs of NnrR. To gain insight into NnrR function, a number of conserved residues were mutagenized. The impact of these changes on NnrR function was assessed by monitoring expression of a nirK-lacZ fusion. In this way a region spanning from Tyr93 to Cys103 that contains residues critical for NnrR activity was identified. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.