X-RAY DIFFRACTION STUDIES OF NUCLEIC ACID STRUCTURES

该项目的总体目标是继续调查 使用X射线晶体学的核酸构象分析 和核磁共振光谱。其他生物物理 技术，如激光拉曼和圆二色光谱 方法，必要时将采用。几个分子系统， 含有精心设计的DNA/RNA寡核苷酸序列 与重要的生物学意义相关，将进行研究， 它们的结构与生物学功能相关。我们建议 为了各种目的研究以下DNA/RNA系统。 （i）.不寻常的核酸构象：几种新的不寻常的核酸 酸构象（例如，Z-DNA，H-DNA，I-DNA，Hoogsteen螺旋，端粒， 最近发现了一些着丝粒。我们会继续研究 这些结构的分子基础，并探索新的和不寻常的 构象 （ii）。具有缺陷的核酸结构。 寡核苷酸与 不同种类的不规则特征，例如不匹配、凸起和 致癌物修饰的碱（例如，m6 G/m4 T，苯并芘加合物）将是 研究了不同的修饰的核苷酸类似物将被掺入到细胞中。 双螺旋，以评估它们对各种 DNA/RNA的交替构象。 （iii）。更高层次的结构。核酸分子可以形成 复杂的三级结构，如三螺旋，发夹，十字形， 假结和圆形分子，所有这些都是重要的， 生物过程（例如，基因调控和重组）。我们 将继续关注发夹和环状DNA的结构。 （iv）。配体-核酸相互作用。核酸的功能 取决于它们与其他分子的相互作用。我们会研究 许多小配体（特别是金属离子）之间的相互作用 和核酸的X射线晶体学。我们将探讨 一些非序列特异性DNA结合蛋白的结晶 (e.g., M13基因V蛋白和HU）及其DNA复合物。 上面描述的那些分子中的相当数量已经在 结构分析的各个阶段。上述范围内的新分子 将合成并通过X射线衍射研究其结构， 匪r列出了各种分子系统的详细描述 在初步结果部分。我们的研究将有助于了解 分子力，控制结构，动力学和能量， 核酸

The overall objective of this project is to continue investigating the conformational diversities of nucleic acids using x-ray crystallography and nuclear magnetic resonance spectroscopy. Other biophysical techniques, such as laser Raman and circular dichroism spectroscopic methods, will be applied when necessary. Several molecular systems, containing carefully-designed DNA/RNA oligonucleotide sequences associated with important biological implications, will be studied and their structures correlated with biological functions. We propose to study the following DNA/RNA systems for various objectives. (i). Unusual nucleic acid con formations: Several new unusual nucleic acid conformations (e.g., Z-DNA, H-DNA, I-DNA, Hoogsteen helix, telomere, centromere) have been uncovered recently. We will continue to study the molecular basis of those structures and to explore new and unusual conformations. (ii). Nucleic acid structure with defects. Oligonucleotides with different kinds of irregular features such as mismatch, bulge and carcinogen-modified base (e.g., m6G/m4T, benzopyrene-adduct) will be studied. Different modified nucleotide analogs will be incorporated into double helix to assess the effect of them on the stability of various alternative DNA/RNA conformations. (iii). Higher-ordered structures. Nucleic acid molecules can form quite complex tertiary structures like triple helix, hairpin, cruciform, pseudoknot and circular molecules, all of which are important in biological processes (e.g., in gene regulation and recombination). We will continue to focus on the structures of hairpins and circular DNA. (iv). Ligand-nucleic acid interactions. The function of nucleic acids depends on their interactions with other molecules. We will study the interactions between a number of small ligands (in particular metal ions) and nucleic acids by x-ray crystallography. We will explore the crystallization of a few non-sequence-specific DNA binding proteins (e.g., M13 gene V protein and HU) and their DNA complexes. A significant number of those molecules described above are already in various stages of structural analysis. New molecules in the above scope will be synthesized and studied structurally by x-ray diffraction and NMR. The detailed descriptions of various molecular systems are listed in the Preliminary Results section. Our studies will help understand the molecular forces that governs the structure, dynamics and energetics of nucleic acids.