AraC proteins with altered DNA sequence specificity which activate a mutant promoter in Escherichia coli.
We examined the recognition of the araBAD promoter by the AraC protein in the Escherichia coli arabinose operon. A mutant promoter, with base substitutions at positions contacted by AraC, was used to isolate suppressor mutations in araC by direct selection. Two hydroxylamine-induced araC mutations were isolated repeatedly; each contained a single amino acid substitution. When tested against a set of base substitution promoter mutants, one revertant, an Arg to His substitution at residue 250, displayed altered base specificity for a single position within the araBAD promoter. The other revertant, a Cys to Tyr substitution at residue 204, did not show consistent base-specific suppression. Neither demonstrated a higher affinity than the wild type protein for the mutant promoter in vitro. Both proteins suppress mutant sequences by a mechanism that does not appear to involve the formation of new net favorable contacts with the mutant base pairs of the promoter.
Francklyn
C S
CS
Department of Biological Sciences, University of California, Santa Barbara 93106.
Lee
N
N
D000483:Alleles; D000595:Amino Acid Sequence; D001089:Arabinose / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D005809:Genes, Regulator; D005797:Genes, araC; D006639:Histidine; D019811:Hydroxylamine; D006898:Hydroxylamines / Q000494:pharmacology; D009154:Mutation; D009876:Operon; D011401:Promoter Regions, Genetic; D013379:Substrate Specificity; D014443:Tyrosine
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D006898:Hydroxylamines; D019811:Hydroxylamine; D014443:Tyrosine; D006639:Histidine; D001089:Arabinose