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Inhibition of Lon‐dependent degradation of the Escherichia coli transcription activator SoxS by interaction with ‘soxbox’ DNA or RNA polymerase
Author(s) -
Shah Ishita M.,
Wolf Richard E.
Publication year - 2006
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2006.05086.x
Subject(s) - regulon , biology , transcription (linguistics) , rna polymerase , microbiology and biotechnology , rna polymerase iii , polymerase , general transcription factor , sigma factor , dna , escherichia coli , rna dependent rna polymerase , biochemistry , promoter , gene expression , gene , linguistics , philosophy
Summary Escherichia coli SoxS, the direct transcription activator of the SoxRS (superoxide) regulon, is intrinsically unstable with an in vivo half‐life of ∼2 min. Overexpression of SoxS is lethal, but mutations interfering with DNA binding relieve the toxicity. Here, we determined the effects on the half‐life of SoxS of alanine substitutions that confer defects in positive control, i.e. transcription activation, or in specific DNA binding. We found that both types of mutations render SoxS more unstable than the wild‐type protein, as if ‘soxbox’ DNA and RNA polymerase serve as stabilizing ligands in vivo that protect SoxS from degradation by Lon, the protease shown previously to be primarily responsible for its turnover. Indeed, we found that the addition of soxbox DNA or RNA polymerase to an in vitro degradation system decreases the rate of SoxS proteolysis by Lon protease. To the best of our knowledge, these are the first examples of target DNA and RNA polymerase serving as ligands that inhibit the turnover of an unstable transcription activator.