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Author Notes:

To whom correspondence should be addressed: Department of Chemistry & Biochemistry, Florida International University, 11200 SW 8th Street, FL 33199. Tel: 305-348-3277; Fax: 305-348-3772; Email: lengf@fiu.edu

FL and DD designed research

GF and DD performed research

PC constructed the molecular model

FL analyzed data

FL wrote the paper

We thank Kathleen S. Matthews for providing us with an E. coli strain overexpressing E. coli lac repressor.


Research Funding:

This study was supported by grants 1SC1HD063059-04 and 1R15GM109254-01A1 from the National Institutes of Health (to F.L.).


  • lac repressor (LacI)
  • DNA loop
  • atomic force microscope (AFM)
  • lac promoter
  • lac operon

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


Journal Title:

FEBS Letters


Volume 590, Number 5


, Pages 613-618

Type of Work:

Article | Post-print: After Peer Review


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.

Copyright information:

© 2017 Federation of European Biochemical Societies

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