Exploring the amino acid residue requirements of the RNA polymerase (RNAP) a subunit C-terminal domain for productive interaction between Spx and RNAP of Bacillus subtilis

Cierra A. Birch, Madison J. Davis, Lea Mbengi, Peter Zuber

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2 Scopus citations


Bacillus subtilis Spx is a global transcriptional regulator that is conserved among Gram-positive bacteria, in which Spx is required for preventing oxidatively induced proteotoxicity. Upon stress induction, Spx engages RNA polymerase (RNAP) through interaction with the C-terminal domain of the rpoA-encoded RNAP α subunit (αCTD). Previous mutational analysis of rpoA revealed that substitutions of Y263 in αCTD severely impaired Spx-activated transcription. Attempts to substitute alanine for αCTD R261, R268, R289, E255, E298, and K294 were unsuccessful, suggesting that these residues are essential. To determine whether these RpoA residues were required for productive Spx-RNAP interaction, we ectopically expressed the putatively lethal rpoA mutant alleles in the rpoAY263C mutant, where "Y263C" indicates the amino acid change that results from mutation of the allele. By complementation analysis, we show that Spx-bound αCTD amino acid residues are not essential for Spx-activated transcription in vivo but that R261A, E298A, and E255A mutants confer a partial defect in NaCl-stress induction of Spx-controlled genes. In addition, strains expressing rpoAE255A are defective in disulfide stress resistance and produce RNAP having a reduced affinity for Spx. The E255 residue corresponds to Escherichia coli αD259, which has been implicated in αCTD-σ70 interaction (σ70 R603, corresponding to R362 of B. subtilis σA). However, the combined rpoAE255A and sigAR362A mutations have an additive negative effect on Spx-dependent expression, suggesting the residues' differing roles in Spx-activated transcription. Our findings suggest that, while αCTD is essential for Spx-activated transcription, Spx is the primary DNA-binding determinant of the Spx-αCTD complex.

Original languageEnglish (US)
Article numbere00124-17
JournalJournal of Bacteriology
Issue number14
Publication statusPublished - Jul 1 2017



  • Alpha subunit
  • RNA polymerase
  • Sporulation
  • Spx
  • Transcription

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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