CHANGES IN CONSERVED REGION-2 OF ESCHERICHIA-COLI SIGMA-70 AFFECTING PROMOTER RECOGNITION

We describe a mutation in rpoD, the gene encoding the σ70 subunit of RNA polymerase, which alters the promoter specificity of the holoenzyme in vivo. The mutant σ causes a substantial and specific increase in the activity of mutant ant and lac promoters with a T · A to C · G substitution at position -12, the first position of the -10 hexamer. The rpoD mutation is a single base-pair substitution causing a Gln → His change at position 437, which is in a domain of conserved region 2.4 that is predicted to form an α-helix. Gln437 would lie one turn of the α-helix away from Thr440, which was previously implicated in recognition of position -12. The rpoD-QH437 mutation described here lends further support to the model that region 2.4 of σ is involved in recognition of the 5′ end of the -10 hexamer. In addition, two rpoD mutations with non-specific effects on promoter recognition are described. © 1990 Academic Press Limited.