Department of Biochemistry, University of Iowa, Iowa City, Iowa, USA.
Electrophoresis. 2023 Sep;44(17-18):1414-1422. doi: 10.1002/elps.202300063. Epub 2023 Jun 24.
The free solution mobilities of 26-base pair (bp) DNA oligomers containing A-tracts with and without internal ApT steps have been measured by capillary electrophoresis, using the mobility of a 26-bp random-sequence oligomer as a reference. The background electrolytes (BGEs) contained mixtures of Li and tetrapropylammonium (TPA ) ions, keeping the total cation concentration constant at 0.3 M. The mobility ratios equaled 1.00 in 0.3 M TPA , indicating that the A-tract and reference oligomers had the same B-form conformation in this BGE. With increasing [Li ], the mobility ratio decreased as Li ions became localized in the A-tract minor groove, suggesting that the A-tract was now in the B* conformation. If the A-tract contained an internal ApT step and the oligomer contained less than ∼50% A + T, the mobility ratio reached a reduced plateau value that remained constant as the [Li ] increased to 0.3 M. However, for A-tracts without an internal ApT step and for A-tracts embedded in oligomers containing more than 50% A + T, the mobility ratios increased again at high [Li ], eventually reaching a plateau value of 1.00. Hence, DNA A-tracts in solution appear to exist as mixtures of the B and B* conformations, with the fractional concentration of each conformer depending on the [Li ], the A-tract sequence, and the total A + T content of the oligomer.
已通过毛细管电泳测量了含有 A-链段的 26 碱基对（bp）DNA 寡聚物和含有内部 ApT 步骤的 26bp 随机序列寡聚物的游离溶液迁移率，以作为参照。背景电解质（BGE）包含锂和四丙基铵（TPA）离子的混合物，使总阳离子浓度在 0.3 M 时保持恒定。在 0.3 M TPA 中，迁移率比等于 1.00，表明 A-链段和参照寡聚物在这种 BGE 中具有相同的 B 型构象。随着[Li]的增加，由于 Li 离子在 A-链段的小沟中局部化，迁移率比降低，表明 A-链段现在处于 B构象。如果 A-链段含有内部 ApT 步骤，并且寡聚物中 A + T 的含量小于约 50%，则迁移率比达到降低的平台值，并且当[Li]增加到 0.3 M 时，该平台值保持不变。然而，对于没有内部 ApT 步骤的 A-链段和嵌入 A + T 含量超过 50%的寡聚物中的 A-链段，在高[Li]下，迁移率比再次增加，最终达到 1.00 的平台值。因此，溶液中的 DNA A-链段似乎作为 B 和 B构象的混合物存在，每种构象的分数浓度取决于[Li]、A-链段序列和寡聚物的总 A + T 含量。
