title: Femtonewton entropic forces can control the formation of protein-mediated DNA loops.
abstract: We show that minuscule entropic forces, on the order of 100 fN, can prevent the formation of DNA loops-a ubiquitous means of regulating the expression of genes. We observe a tenfold decrease in the rate of LacI-mediated DNA loop formation when a tension of 200 fN is applied to the substrate DNA, biasing the thermal fluctuations that drive loop formation and breakdown events. Conversely, once looped, the DNA-protein complex is insensitive to applied force. Our measurements are in excellent agreement with a simple polymer model of loop formation in DNA, and show that an antiparallel topology is the preferred LacI-DNA loop conformation for a generic loop-forming construct.
authors.affiliation: Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Yih-Fan
authors.initials: YF
authors.lastname: Chen
authors.forename: J N
authors.initials: JN
authors.lastname: Milstein
authors.forename: Jens-Christian
authors.initials: JC
authors.lastname: Meiners
mesh_terms: D004269:DNA, Bacterial / Q000737:chemistry* / Q000378:metabolism*; D019277:Entropy; D004926:Escherichia coli / Q000378:metabolism*; D007700:Kinetics; D056968:Lac Repressors / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D009875:Operator Regions, Genetic
chemical_list: D004269:DNA, Bacterial; D056968:Lac Repressors