The bifunctional NadR regulator of Salmonella typhimurium: location of regions involved with DNA binding, nucleotide transport and intramolecular communication.

NadR is the repressor protein that controls the expression of genes for NAD synthesis. It is also believed to be involved in nucleotide transport. Point mutations conferring different phenotypes were localized to six different regions within the nadR gene. That mutations affecting repression and transport all mapped within nadR confirms the bifunctional model for NadR action. The clustering of these mutations and 2 fusions revealed that those affecting repression lie in the amino terminal while those affecting transport occur in the carboxy-terminal. Mutations resulting in superrepression occurred within a central region of NadR that probably senses NAD concentrations. This region is predicted to direct the transition between NadR transport and repressor conformations.