This enzyme has three activities: DNA binding, nicotinamide mononucleotide (NMN) adenylyltransferase and ribosylnicotinamide (RN) kinase. The DNA-binding domain binds to the nadB operator sequence in an NAD- and ATP-dependent manner. As NAD levels increase within the cell, the affinity of NadR for the nadB operator regions of nadA, nadB, and pncB increases, repressing the transcription of these genes. The RN kinase activity catalyzes the phosphorylation of RN to form nicotinamide ribonucleotide. The NMN adenylyltransferase activity catalyzes the transfer of the AMP moiety of ATP to nicotinamide ribonucleotide to form NAD(+). The NMN adenylyltransferase domain also functions as the NAD and ATP sensor. ATP + beta-nicotinamide D-ribonucleotide + H(+) = diphosphate + NAD(+) ATP + beta-nicotinamide D-riboside = ADP + beta-nicotinamide D-ribonucleotide + H(+) Feed-back regulated by NAD. A high level of NAD causes NadR to lose enzymatic activity and repress several NAD synthetic genes; conversely, a low NAD level activates the assimilatory enzymatic activities and leads to derepression of biosynthetic genes (By similarity). Optimum pH is 8.6. Cofactor biosynthesis; NAD(+) biosynthesis [regulation]. Cofactor biosynthesis; NAD(+) biosynthesis; NAD(+) from nicotinamide D-ribonucleotide: step 1/1. Homotetramer. In the central section; belongs to the bacterial NMN adenylyltransferase family. In the C-terminal section; belongs to the bacterial RNK family. Extended N-terminus.