Role of lon and ClpX in the post-translational regulation of a sigma subunit of RNA polymerase required for cellular differentiation in Bacillus subtilis.
The RNA polymerase sigma subunit, sigmaH (Spo0H) of Bacillus subtilis, is essential for the transcription of genes that function in sporulation and genetic competence. Although spo0H is transcriptionally regulated by the key regulatory device that controls sporulation initiation, the Spo0 phosphorelay, there is considerable evidence implicating a mechanism of post-translational control that governs the activity and concentration of sigmaH. Post-translational control of spo0H is responsible for the reduced expression of genes requiring sigmaH under conditions of low environmental pH. It is also responsible for heightened sigmaH activity upon relief of acid stress and during nutritional depletion. In this study, the ATP-dependent proteases LonA and B and the regulatory ATPase ClpX were found to function in the post-translational control of sigmaH. Mutations in lonA and lonB result in elevated sigmaH protein concentrations in low-pH cultures. However, this is not sufficient to increase sigmaH-dependent transcription. Activation of sigmaH-dependent transcription upon raising medium pH and in cells undergoing sporulation requires clpX, as shown by measuring the expression of lacZ fusions that require sigmaH for transcription and by complementation of a clpX null mutation. A hypothesis is presented that low environmental pH results in the Lon-dependent degradation of sigmaH, but the activity of sigmaH in sporulating cells and in cultures at neutral pH is stimulated by a ClpX-dependent mechanism in response to nutritional stress.
Department of Biochemistry and Molecular Biology, Oregon Graduate Institute of Science and Technology, Portland, OR 97291-1000, USA.
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J
Liu
W M
WM
Cosby
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P
Zuber
D049069:ATP-Dependent Proteases; D000074183:ATPases Associated with Diverse Cellular Activities; D000251:Adenosine Triphosphatases / Q000502:physiology*; D001412:Bacillus subtilis / Q000201:enzymology / Q000235:genetics*; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D049071:Endopeptidase Clp; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D018832:Molecular Chaperones; D016297:Mutagenesis, Site-Directed; D011499:Protein Processing, Post-Translational; D012697:Serine Endopeptidases / Q000502:physiology*; D012808:Sigma Factor / Q000096:biosynthesis* / Q000235:genetics; D013171:Spores, Bacterial; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D012808:Sigma Factor; C087737:Spo0H protein, Bacillus subtilis; D014157:Transcription Factors; D049069:ATP-Dependent Proteases; D012697:Serine Endopeptidases; D049071:Endopeptidase Clp; D000251:Adenosine Triphosphatases; C088072:ClpX protein, E coli; D000074183:ATPases Associated with Diverse Cellular Activities