A mutant Escherichia coli sigma 70 subunit of RNA polymerase with altered promoter specificity

J Mol Biol. 1989 Apr 20;206(4):579-90. doi: 10.1016/0022-2836(89)90567-6.


A mutation is described that alters the promoter specificity of sigma 70, the primary sigma factor of Escherichia coli RNA polymerase. In strains carrying both the mutant and wild-type sigma gene (rpoD), the mutant sigma causes a large increase in the activity of mutant P22 ant promoters with A.T or C.G instead of the wild-type, consensus G.C base-pair at position -33, the third position of the consensus -35 hexamer 5'-TTGACA-3'. There is little or no effect on the activities of the wild-type and 23 other mutant ant promoters, including one with T.A at -33. The mutant sigma also activates E. coli lac promoters with A.T or C.G, but not T.A, at the corresponding position. The rpoD mutation (rpoD-RH588) changes a CGT codon to CAT. The corresponding change in sigma 70 is Arg588----His. This residue is in a region that is conserved among most sigma factors, a region that is also homologous with the helix-turn-helix motif of DNA-binding proteins. These results suggest that this region of sigma 70 is directly involved in recognition of the -35 hexamer.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Base Sequence
  • Chromosome Deletion
  • DNA-Directed RNA Polymerases / genetics*
  • Escherichia coli / genetics*
  • Genes, Bacterial
  • Lac Operon
  • Molecular Sequence Data
  • Mutation
  • Promoter Regions, Genetic*
  • Sigma Factor / genetics*
  • Transcription Factors / genetics*


  • Sigma Factor
  • Transcription Factors
  • DNA-Directed RNA Polymerases