Department of Physics, Kent State University, Kent, OH 44242.
Department of Physics, University of Colorado, Boulder, CO 80309.
Proc Natl Acad Sci U S A. 2021 Mar 23;118(12). doi: 10.1073/pnas.2019996118.
Although its mesomorphic properties have been studied for many years, only recently has the molecule of life begun to reveal the true range of its rich liquid crystalline behavior. End-to-end interactions between concentrated, ultrashort DNA duplexes-driving the self-assembly of aggregates that organize into liquid crystal phases-and the incorporation of flexible single-stranded "gaps" in otherwise fully paired duplexes-producing clear evidence of an elementary lamellar (smectic-A) phase in DNA solutions-are two exciting developments that have opened avenues for discovery. Here, we report on a wider investigation of the nature and temperature dependence of smectic ordering in concentrated solutions of various "gapped" DNA (GDNA) constructs. We examine symmetric GDNA constructs consisting of two 48-base pair duplex segments bridged by a single-stranded sequence of 2 to 20 thymine bases. Two distinct smectic layer structures are observed for DNA concentration in the range [Formula: see text] mg/mL. One exhibits an interlayer periodicity comparable with two-duplex lengths ("bilayer" structure), and the other has a period similar to a single-duplex length ("monolayer" structure). The bilayer structure is observed for gap length ≳10 bases and melts into the cholesteric phase at a temperature between 30 °C and 35 °C. The monolayer structure predominates for gap length ≲10 bases and persists to [Formula: see text]C. We discuss models for the two layer structures and mechanisms for their stability. We also report results for asymmetric gapped constructs and for constructs with terminal overhangs, which further support the model layer structures.
尽管其介晶性质已经研究了多年，但直到最近，生命分子才开始揭示其丰富的液晶行为的真正范围。在浓度较高的超短 DNA 双链体之间的端到端相互作用——驱动聚集物自组装成液晶相——以及在其他完全配对双链体中掺入灵活的单链“间隙”——产生了 DNA 溶液中基本层状（向列 A）相的明确证据——这两个令人兴奋的发展为发现开辟了途径。在这里，我们报告了对各种“有间隙”DNA（GDNA）构建体的浓缩溶液中向列有序性的性质和温度依赖性的更广泛研究。我们检查了由两个 48 碱基对双链体片段通过单链序列 2 到 20 个胸腺嘧啶碱基桥接而成的对称 GDNA 构建体。在 [Formula: see text] mg/mL 的 DNA 浓度范围内观察到两种不同的向列层结构。一种表现出与两个双螺旋长度相当的层间周期性（“双层”结构），另一种具有类似于单双螺旋长度的周期性（“单层”结构）。双层结构观察到的间隙长度≳10 个碱基，在 30°C 至 35°C 之间熔化成胆甾相。单层结构主要出现在间隙长度≲10 个碱基的情况下，并持续到 [Formula: see text]C。我们讨论了两种层结构的模型及其稳定性机制。我们还报告了不对称有间隙构建体和具有末端突出的构建体的结果，这些结果进一步支持了模型层结构。
