Escherichia coli lac repressor-lac operator interaction and the influence of allosteric effectors

Nancy Horton, Mitchell Lewis, Ponzy Lu

Research output: Contribution to journalEditorialpeer-review

19 Scopus citations


The wild type E. coli lac operator is embedded in a 35 base-pair DNA sequence containing extensive 2-fold symmetry, suggesting a symmetric repressor operator complex. However, deviations from strict 2-fold symmetry occur at the central base-pair and at three additional base-pairs. Using an operator fragment binding analysis we have determined: (a) a relative contribution each pair provides to the lac repressor-lac operator DNA complex, (b) the operator DNA length necessary for maximum binding to lac repressor; and (c) the contribution of the several non-symmetric base in the wild-type operator to the binding affinity. Since lac repressor-lac operator DNA interaction is reduced upon binding of the gratuitous inducer, isopropyl-β-D-galactoside (IPTG), the same DNA fragment binding analysis was performed with the low affinity form of lac repressor. In the presence of inducer, the affinity for the left half site of the wild-type lac operator is reduced without significant reduction on the right half of the operator. Conversely, the anti-inducer orthonitrophenylfucoside (ONPF) which stabilizes the lac repressor-lac operator complex increases the binding affinity, particularly to the right half of the operator.

Original languageEnglish (US)
Pages (from-to)1-7
Number of pages7
JournalJournal of Molecular Biology
Issue number1
StatePublished - Jan 10 1997


  • Allosteric protein
  • Protein-DNA interaction
  • lac operator
  • lac repressor

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


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