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The repressor for an organic peroxide‐inducible operon is uniquely regulated at multiple levels
Summary ohrR 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 initiat...
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Published in: | Molecular microbiology 2002-05, Vol.44 (3), p.793-802 |
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Main Authors: | , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Summary
ohrR 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 139
bp 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 44 bp 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 processing in 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 per‐oxide. Once the peroxide has been removed, the autoregulation mechanism feeds back to inhibit the expression of the operon. |
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ISSN: | 0950-382X 1365-2958 |
DOI: | 10.1046/j.1365-2958.2002.02919.x |