|NdnR is an NAD-responsive transcriptional repressor of the ndnR operon involved in NAD de novo biosynthesis in Corynebacterium glutamicum.
Microbiology 158: 975-982. 2012.
H. Teramoto, M. Inui and H. Yukawa.
|The Corynebacterium glutamicum ndnR gene, which is chromosomally located in a gene cluster involved in NAD de novo biosynthesis, negatively regulates expression of the cluster genes, i.e.
nadA, nadC, nadS and ndnR itself. Although ndnR encodes a member of the recently identified NrtR family of transcriptional
regulators, whether or not the NdnR protein directly regulates these NAD
biosynthesis genes remains to be verified. Here, two NdnR binding sites
in the promoter region of the ndnR-nadA-nadC-nadS operon in C. glutamicum were confirmed by in vitro DNA binding assay and analysis of in vivo expression of the chromosomally integrated ndnR promoter-lacZ reporter fusion. Electrophoretic mobility shift assay revealed that the
NdnR protein binds to the 5'-upstream region of ndnR, and that the binding is significantly enhanced by NAD. Mutation in two 21 bp NdnR binding motifs in the ndnR promoter region inhibited the binding of NdnR in vitro. The mutation also enhanced the promoter activity in cells cultured in
the presence of nicotinate, which is utilized in NAD biosynthesis, resulting
in the loss of the repression in response to an exogenous NAD precursor;
this is consistent with the effect of deletion of ndnR reported in our previous study. These results indicate that NAD acts as a co-repressor for the NdnR protein that directly regulates the ndnR operon involved in NAD de novo biosynthesis; the NAD-NdnR regulatory system likely plays an important
role in the control of NAD homeostasis in C. glutamicum.