Modifying nucleic acid nanostructures using triplex formation

除了在储存遗传信息方面的天然作用外，DNA还是构建精确三维物体和纳米级组装的绝佳材料。通过使用G与C和A与T的众所周知的碱基配对，可以很容易地设计DNA序列，以便它们组装成这些结构，形成精确的形状。在某些情况下，可以通过简单地将序列一起在盐水中加热并使溶液冷却回室温来实现接近100%的产率。作为一种建筑材料，DNA也相对容易和便宜，以及可生物降解和无毒。DNA已被用于构建能够容纳药物和其他生物分子的容器以及能够响应不同分子信号的装置。下一步是开发一种在这些DNA纳米结构中引入不同化学或生物分子的方法。这将是有用的，例如，在DNA组装中定位不同的组件以生成微小的“纳米”或“生物”芯片，或者将分子引入能够将其靶向特定细胞类型的DNA笼中，然后在那里它可以分配其货物。在这项工作中，我们将开发这样一种方法，利用DNA的能力，形成三链结构。这些三链体结构简单地通过将第三条DNA链添加到现有的双链结构中形成，其中它使用特定的三联体组合连接到正常的碱基对。由于大多数DNA纳米结构是由双链片段构建的，因此可以通过产生这样的三链结构，使用DNA的第三链来识别这些区域。三链体的形成是非常特异的，因此第三条链可以被设计成识别纳米结构内的单个区域。通过将其他分子连接到这条“额外”链上，将有可能将这些分子定位在精确的位置。该策略也可用于将纳米结构连接在一起，或增加现有结构的刚度。这些复合物也可以通过改变条件（即增加pH）容易地分解。我们的方法将为生产许多纳米级结构和器件提供一个新的通用平台，并将使新的超分子结构和材料的设计和合成成为可能。

In addition to its natural role in the storage of genetic information DNA is also an excellent material for constructing precise three-dimensional objects and assemblies on the nano-scale. By using the well-known base pairing of G with C and A with T, sequences of DNA can be easily designed so that they assemble into these structures forming precise shapes. In some cases it is possible to achieve nearly 100% yield by simply heating the sequences together in salty water and allowing the solution to cool back to room temperature. As a construction material DNA is also relatively easy and cheap to make, as well as being biodegradable and non-toxic. DNA has been used to construct containers capable of holding drugs and other biological molecules as well as devices capable of responding to different molecular signals. The next step is to develop a method of introducing different chemical or biological molecules within these DNA nano-structures. This would be useful, for example, in positioning different components within a DNA assembly to generate tiny 'nano' or 'bio' chips or to introduce a molecule onto a DNA cage capable of targeting it to a specific cell type, where it could then dispense its cargo. In this work we will develop such a method by exploiting the capacity of DNA to form three-stranded structures. These triplex structures are simply formed by adding a third strand of DNA to an existing double-stranded structure, where it attaches to the normal base pairs using specific triplet combinations. As the majority of DNA nano-structures are constructed from double-stranded segments it is possible to recognise these regions using a third strand of DNA, by generating a such three-stranded structure. Triplex formation is exquisitely specific and the third strand can therefore be designed to recognise a single region within a nanostructure. By attaching other molecules to this 'extra' strand it will be possible to position these at precise locations. The strategy can also be used to join nano-structures together, or to increase the rigidity of an existing structure. These complexes can also be easily disassembled by changing the conditions (i.e. increasing the pH). Our approach will offer a new general platform for producing many nanometer-scale structures and devices and will enable the design and synthesis of new supramolecular structures and materials.