|OxyR acts as a transcriptional repressor of hydrogen peroxide-inducible
antioxidant genes in Corynebacterium glutamicum R.
FEBS J. 280: 3298-3312. 2013.
H. Teramoto, M. Inui and H. Yukawa.
|OxyR, a LysR-type transcriptional regulator, has been established as a
redox-responsive activator of antioxidant genes in bacteria. This study
shows that OxyR acts as a transcriptional repressor of katA, dps, ftn and cydA in Corynebacterium glutamicum R. katA encodes H2 O2 -detoxifing enzyme catalase, dps and ftn are implicated in iron homeostasis and cydA encodes a subunit of cytochrome bd oxidase. Quantitative RT-PCR analyses revealed that expression of katA and dps, but not of ftn and cydA, was induced by H2 O2 . Disruption of the oxyR gene encoding OxyR resulted in a marked increase in katA and dps mRNAs to a level higher than that induced by H2 O2 , and the oxyR-deficient mutant showed a H2 O2 -resistant phenotype. This is in contrast to the conventional OxyR-dependent
regulatory model. ftn and cydA were also upregulated by oxyR disruption but to a smaller extent. Electrophoretic mobility shift assays
revealed that the OxyR protein specifically binds to all four upstream
regions of the respective genes under reducing conditions. We observed
that the oxidized form of OxyR similarly bound to not only the target promoter
regions, but also nonspecific DNA fragments. Based on these findings, we
propose that the transcriptional repression by OxyR is alleviated under
oxidative stress conditions in a titration mechanism due to the decreased
specificity of its DNA-binding activity. DNase I footprinting analyses
revealed that the OxyR-binding site in the four target promoters is ~ 50
bp in length and has multiple T-N11 -A motifs, a feature of LysR-type transcriptional regulators, but no significant
overall sequence conservation.