Skorn MongkolsukWarunya PanmaneeSopapan AtichartpongkulPaiboon VattanaviboonWirongrong WhangsukMayuree FuangthongWarawan EiamphungpornRojana SukchawalitSupa UtamapongchaiChulabhorn Research InstituteMahidol UniversityCornell UniversityUniversity of Birmingham2018-07-242018-07-242002-05-28Molecular Microbiology. Vol.44, No.3 (2002), 793-8020950382X2-s2.0-0036096988https://repository.li.mahidol.ac.th/handle/20.500.14594/20064ohrR encodes a novel organic peroxide-inducible transcription repressor, and we have demonstrated that ohrR is regulated at the transcriptional and the post-transcriptional levels. Primer extension results show that ohrR transcription initiates at the A residue of the ATG translation initiation codon for the ohrR coding sequence. Thus, the gene has a leaderless mRNA. The ohrR promoter (P1) has high homology to the consensus sequence for Xanthomonas promoters, which is reflected in the high in vivo promoter activity of P1. Deletion of a 139bp fragment containing the P1 promoter showed that the sequences upstream of -35 regions were required for neither the promoter activity nor OhrR autoregulation. In vitro, purified OhrR specifically binds to the P1 promoter. DNase I footprinting of OhrR binding to the P1 revealed a 44bp region of protection on both DNA strands. The protected regions include the -35 and -10 regions of P1. We suggest that OhrR represses gene expression by blocking RNA polymerase binding to the promoter. There are two steps in the post-transcriptional regulation of ohrR, namely differential stability and inefficient translation of the mRNA. The bicistronic ohrR-ohr mRNA was highly labile and underwent rapid processingin vivo to give only stable monocistronic ohr mRNA and undetectable ohrR mRNA. Furthermore, the ohrR mRNA was inefficiently translated. We propose that, in uninduced cells, the concentration of OhrR is maintained at low levels by the autoregulation mechanism at the transcriptional levels and by the ohrR mRNA instability coupled with inefficient translation at the post-transcriptional level. Upon exposure to an organic peroxide, the compound probably interacts with OhrR and prevents it from repressing the P1 promoter, thus allowing high-level expression of the ohrR-ohr operon. The rapid processing of bicistronic mRNA gives highly stable ohr mRNA and corresponding high levels of Ohr, which remove an organic peroxide. Once the peroxide has been removed, the autoregulation mechanism feeds back to inhibit the expression of the operon.Mahidol UniversityBiochemistry, Genetics and Molecular BiologyImmunology and MicrobiologyArticleSCOPUS10.1046/j.1365-2958.2002.02919.x