title: Stretched and overwound DNA forms a Pauling-like structure with exposed bases.
abstract: We investigate structural transitions within a single stretched and supercoiled DNA molecule. With negative supercoiling, for a stretching force >0.3 pN, we observe the coexistence of B-DNA and denatured DNA from sigma approximately -0.015 down to sigma = -1. Surprisingly, for positively supercoiled DNA (sigma > +0.037) stretched by 3 pN, we observe a similar coexistence of B-DNA and a new, highly twisted structure. Experimental data and molecular modeling suggest that this structure has approximately 2.62 bases per turn and an extension 75% larger than B-DNA. This structure has tightly interwound phosphate backbones and exposed bases in common with Pauling's early DNA structure [Pauling, L. & Corey, R. B. (1953), Proc. Natl. Acad. Sci. USA 39, 84-97] and an unusual structure proposed for the Pf1 bacteriophage [Liu, D. J. & Day, L. A. (1994) Science 265, 671-674].
authors.affiliation: Laboratoire de Physique Statistique, Ecole Normale Supérieure, Unité de Recherche Associée D 1306 Centre National de la Recherche Scientifique, Paris Cedex 05, France.allemand@physique.ens.fr
authors.forename: J F
authors.initials: JF
authors.lastname: Allemand
authors.forename: D
authors.initials: D
authors.lastname: Bensimon
authors.forename: R
authors.initials: R
authors.lastname: Lavery
authors.forename: V
authors.initials: V
authors.lastname: Croquette
mesh_terms: D000906:Antibodies; D001710:Biotin; D019921:Biotinylation; D004247:DNA / Q000737:chemistry*; D004076:Digoxigenin / Q000276:immunology; D005898:Glass; D006037:Glyoxal / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D013314:Stress, Mechanical
chemical_list: D000906:Antibodies; D006037:Glyoxal; D001710:Biotin; D004247:DNA; D004076:Digoxigenin