DNR (Dissimilative Nitrate Respiration regulator) protein is part of the Pseudomonas aeruginosa denitrification pathway. Under low oxygen tensions, Pseduomonas can convert nitrate to nitrogen through a four-step reduction process. DNR is the transcription factor that regulates the expression of NarK/G, NorCB, and NirS - the enzymes that catalyze denitrification. In addition to being cooperatively activated by ANR and NarXL, nitric oxide must also be present for DNR to induce transcription. DNR is a part of the Crp-Fnr superfamily of proteins, similar to CooA, and appears to use an analogous allosteric control mechanism. Based on domain homology, its ability to sense NO, as well as other recent studies, DNR probably contains a heme group which it uses to transfer binding of NO information into a conformation change to allow DNA binding. However, only the apo-form of DNR has been expressed and characterized to date.