Point Mutations That Reduce the Expression of malPQ, a Positively Controlled Operon of Escherichia Coli

J Mol Biol. 1984 Jul 25;177(1):69-86. doi: 10.1016/0022-2836(84)90058-5.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Chromosome Mapping
  • DNA, Bacterial
  • Escherichia coli / genetics*
  • Gene Expression
  • Gene Expression Regulation*
  • Maltose / genetics*
  • Mutation
  • Operon*
  • Phenotype


  • DNA, Bacterial
  • Maltose

Associated data

  • GENBANK/M10620