Molecular model of the organic hydroperoxide resistance repressor protein (ohrR, green) binding to a region of DNA (deoxyribonucleic acid, pink and purple) known as the organic hydroperoxide resistance A (ohrA) operator from the Bacillus subtilis bacterium. OhrA codes for proteins that protect the bacteria against damaging hydroperoxide molecules. The repressor protein acts to turn off transcription, inhibiting the expression of the genes, when there are no hydroperoxide molecules present.