J Phys Condens Matter. 2010 Dec 15;22(49):494110. doi: 10.1088/0953-8984/22/49/494110.
Transient electric birefringence has been used to quantify the curvature of two DNA restriction fragments, a 199-base-pair fragment taken from the origin of replication of the M13 bacteriophage and a 207-base-pair fragment taken from the VP1 gene in the SV40 minichromosome. Stable curvature in the SV40 and M13 restriction fragments is due to a series of closely spaced A tracts, runs of 4-6 contiguous adenine residues located within 40 or 60 base pair 'curvature modules' near the center of each fragment. The M13 and SV40 restriction fragments exhibit bends of ∼ 45° in solutions containing monovalent cations and ∼ 60° in solutions containing Mg(2 +) ions. The curvature is not localized at a single site but is distributed over the various A tracts in the curvature modules. Thermal denaturation studies indicate that the curvature in the M13 and SV40 restriction fragments remains constant up to 30 °C in solutions containing monovalent cations, and up to 40 °C in solutions containing Mg(2 +) ions, before beginning to decrease slowly with increasing temperature. Hence, stable curvature in these DNA restriction fragments exists at the biologically important temperature of 37 °C.
瞬时电双折射已被用于定量测量两个 DNA 限制片段的曲率，一个片段是从 M13 噬菌体复制起点提取的 199 个碱基对，另一个片段是从 SV40 微染色体的 VP1 基因提取的 207 个碱基对。SV40 和 M13 限制片段的稳定曲率是由于一系列紧密间隔的 A 链，这些 A 链位于每个片段中心附近的 40 或 60 个碱基对的“曲率模块”中，由 4-6 个连续的腺嘌呤残基组成。在含有单价阳离子的溶液中，M13 和 SV40 限制片段的弯曲度约为 45°，在含有 Mg(2+)离子的溶液中，弯曲度约为 60°。这种曲率不是局限于一个单一的位置，而是分布在曲率模块中的各个 A 链上。热变性研究表明，在含有单价阳离子的溶液中，M13 和 SV40 限制片段的曲率在 30°C 以下保持不变，在含有 Mg(2+)离子的溶液中，在 40°C 以下保持不变，然后随着温度的升高缓慢下降。因此，在这些 DNA 限制片段中，稳定的曲率存在于生物学上重要的 37°C 温度下。
