Inhibition of Escherichia coli RNA polymerase by bacteriophage T4 AsiA

Elena Severinova, Konstantin Severinov, Seth A. Darst

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79 Scopus citations


The 10 kDa bacteriophage T4 antisigma protein AsiA binds the Escherichia coli RNA polymerase promoter specificity subunit, σ70, with high affinity and inhibits its transcription activity. AsiA binds to σ70 primarily through an interaction with conserved region 4.2, which has also been implicated in sequence-specific recognition of the -35 consensus promoter element. Here we show that AsiA forms a stable ternary complex with core RNA polymerase (RNAP) and σ70 and thus does not inhibit σ70 activity by preventing its binding to core RNAP. We investigated the effect of AsiA on open promoter complex formation and abortive initiation at two -10/-35 type promoters and two 'extended -10' promoters. Our results indicate that the binding of AsiA to σ70 and the interaction of σ70 region 4.2 with the -35 consensus promoter element of -10/-35 promoters is mutually exclusive. In contrast, AsiA has much less effect on open promoter complex formation and abortive initiation from extended -10 promoters, which lack a -35 consensus element and do not require σ70 conserved region 4.2. From these results we conclude that T4 AsiA inhibits E. coli RNAP σ70 holoenzyme transcription at -10/ -35 promoters by interfering with the required interaction between σ70 conserved region 4.2 and the -35 consensus promoter element.

Original languageEnglish (US)
Pages (from-to)9-18
Number of pages10
JournalJournal of molecular biology
Issue number1
StatePublished - May 29 1998
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Structural Biology
  • Molecular Biology


  • Bacteriophage T4 antisigma
  • E. coli RNA polymerase
  • Transcription


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