This enzyme has two activities: nicotinamide mononucleotide (NMN) adenylyltransferase and ribosylnicotinamide (RN) kinase. 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(+). ATP + beta-nicotinamide D-ribonucleotide + H(+) = diphosphate + NAD(+) ATP + beta-nicotinamide D-riboside = ADP + beta-nicotinamide D-ribonucleotide + H(+) Feed-back regulated by NAD. At high levels of NAD the RN kinase activity is inhibited. Cofactor biosynthesis; NAD(+) biosynthesis [regulation]. Cofactor biosynthesis; NAD(+) biosynthesis; NAD(+) from nicotinamide D-ribonucleotide: step 1/1. Homotetramer. Found as a soluble cytoplasmic protein as well as a membrane-associated protein. In combination with corepressor (NAD), the cytoplasmic form of NadR would be capable of acting as a transcriptional repressor. Shows the same catalytic activity as isoform Long. In the N-terminal section; belongs to the bacterial NMN adenylyltransferase family. In the C-terminal section; belongs to the bacterial RNK family.