期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1997
卷号：94
期号：2
页码：496-501
DOI：10.1073/pnas.94.2.496
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：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 (AFM in 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.
