title: Video light microscopy of 670-kb DNA in a hanging drop: shape of the envelope of DNA.
abstract: Although its conformation has not been observed directly, double-stranded DNA in solution is usually assumed to be randomly coiled at the level of the DNA double helix. By video light microscopy of ethidium-stained DNA at equilibrium in a nonturbulent hanging drop, in the present study, the 670 kb linear bacteriophage G DNA is found to form a flexible filament that has on average 17 double helical segments across its width. This flexible filament 1) has both asymmetry and dimensions expected of a random coil and 2) has ends that move according to the statistics expected of a random walk. After unraveling the flexible filament-associated DNA double helix near the surface of a hanging drop, recompaction occurs without perceptible rotation of the DNA. Both conformational change and intermolecular tangling of the DNA are observed when G DNA undergoes nondiffusive motion in a hanging drop. The characteristics of the G DNA flexible filament are explained by the assumption that the flexible filament is a random coil of double helical segments that are unperturbed by motion of the suspending medium.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760, USA. serwer@uthscsa.edu
authors.forename: P
authors.initials: P
authors.lastname: Serwer
authors.forename: A
authors.initials: A
authors.lastname: Estrada
authors.forename: R A
authors.initials: RA
authors.lastname: Harris
mesh_terms: D001435:Bacteriophages; D001482:Base Composition; D003198:Computer Simulation; D004279:DNA, Viral / Q000737:chemistry* / Q000648:ultrastructure*; D004587:Electrophoresis, Agar Gel; D004996:Ethidium; D008856:Microscopy, Fluorescence / Q000379:methods; D018715:Microscopy, Video / Q000379:methods; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D011897:Random Allocation
chemical_list: D004279:DNA, Viral; D004996:Ethidium