HucR, a Novel Uric Acid-responsive Member of the MarR Family of Transcriptional Regulators from Deinococcus radiodurans

The MarR family of transcriptional regulators comprises a subset of winged helix DNA-binding proteins and includes numerous members that function in environmental surveillance of aromatic compounds. We describe the characterization of HucR, a novel MarR homolog from Deinococcus radiodurans that demonstrates phenolic sensing capabilities. HucR binds as a homodimer to a single site within its promoter/operator region with Kd = 0.29 ± 0.02 nm. The HucR binding site contains a pseudopalindromic sequence, composed of 8-bp half-sites separated by 2 bp. The location of the HucR binding site in the intergenic region between hucR and a putative uricase suggests a mechanism of simultaneous co-repression of these two genes. The substrate of uricase, uric acid, is an efficient antagonist of DNA binding, reducing HucR-DNA complex formation to 50% at 0.26 mm ligand, compared with 5.2 and 46 mm for the aromatic compounds salicylate and acetylsalicylate, respectively. Enhanced levels in vivo of hucR and uricase transcript and increased uricase activity under conditions of excess uric acid further indicate a novel regulatory mechanism of aromatic catabolism in D. radiodurans. Since uric acid is a scavenger of reactive oxygen species, we hypothesize that HucR is a participant in the intrinsic resistance of D. radiodurans to high levels of oxidative stress.