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Updated: Mar 25, 2026

Studying DNA Looping by Single-Molecule FRET
Published on: June 28, 2014
Direct observation of a 91 bp LacI-mediated, negatively supercoiled DNA loop by atomic force microscope
Geraldine Fulcrand1,2, Prem Chapagain1,3, David Dunlap4
1Biomolecular Sciences Institute, Florida International University, Miami, FL, USA.
Abstract:
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.
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