title: Visualizing the formation and collapse of DNA toroids.
abstract: In living organisms, DNA is generally confined into very small volumes. In most viruses, positively charged multivalent ions assist the condensation of DNA into tightly packed toroidal structures. Interestingly, such cations can also induce the spontaneous formation of DNA toroids in vitro. To resolve the condensation dynamics and stability of DNA toroids, we use a combination of optical tweezers and fluorescence imaging to visualize in real-time spermine-induced (de)condensation in single DNA molecules. By actively controlling the DNA extension, we are able to follow (de)condensation under tension with high temporal and spatial resolution. We show that both processes occur in a quantized manner, caused by individual DNA loops added onto or removed from a toroidal condensate that is much smaller than previously observed in similar experiments. Finally, we present an analytical model that qualitatively captures the experimentally observed features, including an apparent force plateau.
authors.affiliation: Department of Physics and Astronomy and Laser Centre, VU University, Amsterdam, The Netherlands. bramvdbroek@physics.leidenuniv.nl
authors.forename: Bram
authors.initials: B
authors.lastname: van den Broek
authors.forename: Maarten C
authors.initials: MC
authors.lastname: Noom
authors.forename: Joost
authors.initials: J
authors.lastname: van Mameren
authors.forename: Christopher
authors.initials: C
authors.lastname: Battle
authors.forename: Fred C
authors.initials: FC
authors.lastname: Mackintosh
authors.forename: Gijs J L
authors.initials: GJ
authors.lastname: Wuite
mesh_terms: D010582:Bacteriophage lambda; D001696:Biomechanical Phenomena; D004279:DNA, Viral / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry; D052898:Optical Tweezers; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D004279:DNA, Viral; D005456:Fluorescent Dyes