title: Mutations in rpoD, the gene encoding the sigma 70 subunit of Escherichia coli RNA polymerase, that increase expression of the lac operon in the absence of CAP-cAMP.
abstract: We have isolated a new class of mutations in rpoD, the gene encoding the sigma 70 subunit of Escherichia coli RNA polymerase, that alter the transcription initiation properties of RNA polymerase holoenzyme. The rpoD(Lac) mutations increase expression of the lac operon in the absence of CAP-cAMP, allowing a strain lacking adenyl cyclase to grow on lactose. Four of the six alleles isolated have three- to fivefold increases in the amount of lac mRNA and beta-galactosidase per cell. We show that these four mutations increase transcription initiation from the same promoter used by wild-type RNA polymerase. The mutations were mapped and sequenced. One mutation occurs in the codon for amino acid 389 of the sigma 70 polypeptide. The remaining five mutations are clustered, affecting residues 570, 571 and 575. These five mutations are within or near a proposed helix-turn-helix motif in the C terminus of sigma 70.
authors.affiliation: Department of Bacteriology, University of Wisconsin, Madison 53706.
authors.forename: D A
authors.initials: DA
authors.lastname: Siegele
authors.forename: J C
authors.initials: JC
authors.lastname: Hu
authors.forename: C A
authors.initials: CA
authors.lastname: Gross
mesh_terms: D000595:Amino Acid Sequence; D002874:Chromosome Mapping; D000242:Cyclic AMP; D012321:DNA-Directed RNA Polymerases / Q000235:genetics*; D004926:Escherichia coli; D005786:Gene Expression Regulation; D005798:Genes, Bacterial; D007763:Lac Operon; D008969:Molecular Sequence Data; D009154:Mutation; D014158:Transcription, Genetic
chemical_list: D000242:Cyclic AMP; D012321:DNA-Directed RNA Polymerases