Protein-mediated looping of DNA under tension requires supercoiling. Issue 5 (22nd January 2018)

• Record Type: Journal Article
• Authors: Yan, Yan; Leng, Fenfei; Finzi, Laura; Dunlap, David
• Is Part Of: Nucleic acids research. Volume 46:Issue 5(2018)
• Page Start: 2370
• Page End: 2379
• Publication Date: 2018-01-22
• Subjects: Nucleic acids -- Periodicals; Molecular biology -- Periodicals; 572.805
• DOI: 10.1093/nar/gky021
• Languages: English
• ISSNs: 0305-1048

Abstract

Abstract: Protein-mediated DNA looping is ubiquitous in chromatin organization and gene regulation, but to what extent supercoiling or nucleoid associated proteins promote looping is poorly understood. Using the lac repressor (LacI), a paradigmatic loop-mediating protein, we measured LacI-induced looping as a function of either supercoiling or the concentration of the HU protein, an abundant nucleoid protein in Escherichia coli . Negative supercoiling to physiological levels with magnetic tweezers easily drove the looping probability from 0 to 100% in single DNA molecules under slight tension that likely exists in vivo . In contrast, even saturating (micromolar) concentrations of HU could not raise the looping probability above 30% in similarly stretched DNA or 80% in DNA without tension. Negative supercoiling is required to induce significant looping of DNA under any appreciable tension.