Direct observation of a 91 bp LacI-mediated, negatively supercoiled DNA loop by atomic force microscope

FEBS Lett. 2016 Mar;590(5):613-8. doi: 10.1002/1873-3468.12094. Epub 2016 Feb 26.


Escherichia coli lactose repressor (LacI), a tetrameric protein, is a paradigmatic transcriptional factor that controls the expression of lacZYA in the lac operon. It specifically binds to the O1, O2, and O3 operators of the lac promoter, forms DNA loops, and regulates transcription of the lac operon. In this article, utilizing combined techniques of DNA-nicking assay and AFM imaging, we directly observed a 91 bp LacI-mediated, negatively supercoiled DNA loop mimicking the DNA loop between the O1 and O3 operators in the lac promoter.

Keywords: DNA loop; atomic force microscope; the lac operon; the lac promoter; the lac repressor.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • DNA, Superhelical / chemistry*
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism*
  • Lac Repressors / chemistry
  • Lac Repressors / metabolism*
  • Microscopy, Atomic Force*
  • Models, Molecular
  • Nucleic Acid Conformation
  • Protein Conformation


  • DNA, Superhelical
  • Escherichia coli Proteins
  • Lac Repressors
  • LacI protein, E coli