title: Point mutations that reduce the expression of malPQ, a positively controlled operon of Escherichia coli.
abstract: malPQ is one of three operons controlled by the positive regulator gene malT. With the objective of defining DNA sequences essential for malPQ transcription, we looked for cis-dominant mutations that reduced the level of expression of this operon. We first constructed malP-lac fusion strains, selected from one of them a series of mutants resistant to p-nitrophenyl-beta-D-thiogalactopyranoside (a bacteriostatic compound that enters the cells via lac permease), and retained the clones that contained a mutation reducing the expression of the hybrid operon in a cis-dominant fashion. Nineteen such mutations were sequenced, and their effect on an otherwise wild type malPQ operon was studied. Three of them mapped in a transcribed portion of the operon, and are believed to exert their effect at the translation level. The others map upstream from the transcription startpoint (co-ordinate +1) and help define three DNA segments that must play a predominant role in transcription initiation: the Pribnow box (from positions -7 to -12); and two inverted repeats, extending from position -32 to -36, and -59 to -63, respectively, which are proposed to constitute part of the binding site for MalT protein.
mesh_terms: D001483:Base Sequence; D002874:Chromosome Mapping; D004269:DNA, Bacterial; D004926:Escherichia coli / Q000235:genetics*; D015870:Gene Expression; D005786:Gene Expression Regulation; D008320:Maltose / Q000235:genetics*; D009154:Mutation; D009876:Operon; D010641:Phenotype
chemical_list: D004269:DNA, Bacterial; D008320:Maltose