Open AccessVisualization of supercoiled DNA with atomic force microscopy in situ
Author(s) -
Yuri L. Lyubchenko,
Luda S. Shlyakhtenko
Publication year - 1997
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.94.2.496
Subject(s) - visualization , in situ , atomic force microscopy , dna supercoil , dna , microscopy , biophysics , chemistry , computational biology , nanotechnology , materials science , crystallography , biology , physics , computer science , optics , biochemistry , data mining , dna replication , organic chemistry
Tertiary structure of supercoiled DNA is a significant factor in a number of genetic functions and is apparently affected by environmental conditions. We applied atomic force microscopy (AFM) for imaging the supercoiled DNA deposited at different ionic conditions. We have employed a technique for the sample preparation that permits high-resolution AFM imaging of DNA bound to the surface in buffer solutions without drying the sample (AFMin situ ). The AFM data show that at low ionic strength, DNA molecules are loosely interwound supercoils with an irregular shape. Plectonemic superhelices are formed in high-concentration, near-physiological salt solutions. At such ionic conditions, superhelical loops are typically separated by regions of close helix–helix contacts. The data obtained show directly and unambiguously that overall geometry of supercoiled DNA depends dramatically on ionic conditions. This fact and the formation of close contacts between DNA helices are important features of supercoiled DNA related to its biological functions.