Niacin-mediated Gene Expression and Role of NiaR as a Transcriptional Repressor of , and in .

NAD (Nicotinamide Adenine Dinucleotide) biosynthesis is vital for bacterial physiology and plays an important role in cellular metabolism. A naturally occurring vitamin B complex, niacin (nicotinic acid), is a precursor of coenzymes NAD and NADP. Here, we study the impact of niacin on global gene expression of D39 and elucidate the role of NiaR as a transcriptional regulator of , and . Transcriptome comparison of the D39 wild-type grown in chemically defined medium (CDM) with 0 to 10 mM niacin revealed elevated expression of various genes, including , and that are putatively involved in the transport and utilization of niacin. Niacin-dependent expression of these genes is confirmed by promoter fusion studies. Moreover, the role of transcriptional regulator NiaR in the regulation of these genes is explored by DNA microarray analysis. Our transcriptomic comparison of D39 Δ to D39 wild-type revealed that the transcriptional regulator NiaR acts as a transcriptional repressor of , and . NiaR-dependent regulation of , and is further confirmed by promoter fusion studies. The putative operator site of NiaR (5'-TACWRGTGTMTWKACASYTRWAW-3') in the promoter regions of , and is predicted and further confirmed by promoter mutational experiments.