The lac repressor

C R Biol. 2005 Jun;328(6):521-48. doi: 10.1016/j.crvi.2005.04.004.


Few proteins have had such a strong impact on a field as the lac repressor has had in Molecular Biology. Over 40 years ago, Jacob and Monod [Genetic regulatory mechanisms in the synthesis of proteins, J. Mol. Biol. 3 (1961) 318] proposed a model for gene regulation, which survives essentially unchanged in contemporary textbooks. It is a cogent depiction of how a set of 'structural' genes may be coordinately transcribed in response to environmental conditions and regulates metabolic events in the cell. In bacteria, the genes required for lactose utilization are negatively regulated when a repressor molecule binds to an upstream cis activated operator. The repressor and its operator together form a genetic switch, the lac operon. The switch functions when inducer molecules alter the conformation of the repressor in a specific manner. In the presence of a particular metabolite, the repressor undergoes a conformational change that reduces its affinity for the operator. The structures of the lac repressor and its complexes with operator DNA and effector molecules have provided a physical platform for visualizing at the molecular level the different conformations the repressor and the molecular basis for the switch. The structures of lac repressor, bound to its operator and inducer, have also been invaluable for interpreting a plethora of biochemical and genetic data.

Publication types

  • Historical Article
  • Review

MeSH terms

  • Allosteric Site
  • Animals
  • Bacterial Proteins* / chemistry
  • Bacterial Proteins* / genetics
  • Bacterial Proteins* / history
  • Bacterial Proteins* / metabolism
  • Binding Sites
  • DNA / metabolism
  • Dimerization
  • Escherichia coli / genetics
  • Escherichia coli Proteins
  • History, 20th Century
  • Lac Operon
  • Lac Repressors
  • Mice
  • Models, Molecular
  • Molecular Structure
  • Mutagenesis
  • Repressor Proteins* / chemistry
  • Repressor Proteins* / genetics
  • Repressor Proteins* / history
  • Repressor Proteins* / metabolism
  • Structure-Activity Relationship


  • Bacterial Proteins
  • Escherichia coli Proteins
  • Lac Repressors
  • LacI protein, E coli
  • Repressor Proteins
  • DNA