DNA A-tracts Are Not Curved in Solutions Containing High Concentrations of Monovalent Cations

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• 作者：Earle Stellwagen ; Justin P. Peters ; L. James Maher ; III ; Nancy C. Stellwagen
• 刊名：Biochemistry
• 出版年：2013
• 出版时间：June 18, 2013
• 年：2013
• 卷：52
• 期：24
• 页码：4138-4148
• 全文大小：462K
• 年卷期：v.52,no.24(June 18, 2013)
• ISSN：1520-4995

文摘

The intrinsic curvature of seven 98 bp DNA molecules containing up to four centrally located A₆-tracts has been measured by gel and capillary electrophoresis as a function of the number and arrangement of the A-tracts. At low cation concentrations, the electrophoretic mobility observed in polyacrylamide gels and in free solution decreases progressively with the increasing number of phased A-tracts, as expected for DNA molecules with increasingly curved backbone structures. Anomalously slow electrophoretic mobilities are also observed for DNA molecules containing two pairs of phased A-tracts that are out of phase with each other, suggesting that out-of-phase distortions of the helix backbone do not cancel each other out. The mobility decreases observed for the A-tract samples are due to curvature, not cation binding in the A-tract minor groove, because identical free solution mobilities are observed for a molecule with four out-of-phase A-tracts and one with no A-tracts. Surprisingly, the curvature of DNA A-tracts is gradually lost when the monovalent cation concentration is increased to 200 mM, regardless of whether the cation is a hydrophilic ion like Na⁺, NH₄⁺, or Tris⁺ or a hydrophobic ion like tetrabutylammonium. The decrease in A-tract curvature with increasing ionic strength, along with the known decrease in A-tract curvature with increasing temperature, suggests that DNA A-tracts are not significantly curved under physiological conditions.