Activates transcription of the denitrifying genes (nitrate reductase narA and nitrite reductase nirK) under anaerobic conditions. Constitutively expressed regardless of cultivation under aerobic or anaerobic conditions. Increased expression under denitrifying conditions. Cells lacking this gene are not able to grow anaerobically by denitrification. Inactivated transcription of the denitrifying genes (nitrate reductase narA and nitrite reductase nirK). No effect on growth under aerobic conditions. No effect on dimethyl sulfoxide (DMSO) respiration.