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Probing transcription factor dynamics at the single-molecule level in a living cell.

Transcription factors regulate gene expression through their binding to DNA. In a living Escherichia coli cell, we directly observed specific binding of a lac repressor, labeled with a fluorescent protein, to a chromosomal lac operator. Using single-molecule detection techniques, we measured the kinetics of binding and dissociation of the repressor in response to metabolic signals. Furthermore, we characterized the nonspecific binding to DNA, one-dimensional (1D) diffusion along DNA segments, and 3D translocation among segments through cytoplasm at the single-molecule level. In searching for the operator, a lac repressor spends approximately 90% of time nonspecifically bound to and diffusing along DNA with a residence time of <5 milliseconds. The methods and findings can be generalized to other nucleic acid binding proteins.

Pubmed ID: 17525339


  • Elf J
  • Li GW
  • Xie XS


Science (New York, N.Y.)

Publication Data

May 25, 2007

Associated Grants

  • Agency: NIH HHS, Id: DP1 OD000277
  • Agency: NIH HHS, Id: DP1 OD000277-02

Mesh Terms

  • Bacterial Proteins
  • DNA, Bacterial
  • Diffusion
  • Escherichia coli
  • Escherichia coli Proteins
  • Kinetics
  • Lac Operon
  • Lac Repressors
  • Luminescent Proteins
  • Microscopy, Fluorescence
  • Operator Regions, Genetic
  • Protein Binding
  • Repressor Proteins
  • Signal Transduction