UNUSUAL NUCLEIC ACID STRUCTURES IN BIOLOGY

这项建议的目的是完善和扩大我们的结构， 研究我们最近发现的一种新的结构基序， “剪切GA括号未配对G堆栈”。人类着丝粒的重复序列 五聚体DNA序列TGGAA与自身形成稳定的双链体， 其中“自互补”[GGA]2基序由AT和TA分开， 沃森-克里克对。（GGA]2基序由剪切的GA和AG对组成 其包含两个不成对但共堆叠（插入）的鸟苷， 形成GGGG堆栈。重复的（TGGAA）n序列出现在染色体上 在染色单体的分离中可能是重要的 在有丝分裂中。 我们希望研究除鸟苷以外的残基的能力， 堆叠在剪切的G：A-A：G夹层中，并研究改变 侧翼的TA和AT对的结构和稳定性的影响， 重复五聚体序列中的内部[GNA]2基序。我们还将研究 四种GNA序列采用剪切不成对叠加的能力 [（GNA）n]2个结构，当彼此紧邻放置时， 串联阵列，即没有插入AT和TA沃森-克里克对 这一结果对于研究重复的机制具有重要意义 三重重复疾病的扩展肌肉营养不良，肌肉 萎缩和亨廷顿病-所有这些似乎都是（GCA）n 重复。我们还将研究在脆性X婴儿中发现的（GCG）n重复序列 智力迟钝。 [GGA]2基序的结构和稳定性，有和没有额外的 环出残基，也将在短RNA“内部”中进行研究。 环”，其中它们可能涉及核酶功能，逆转录病毒 识别和逆转录病毒二聚化。几种富含嘌呤的DNA和RNA 我们预计从调查中出现的发夹也将被研究， 750 MHz高分辨率NMR。

The objectives of this proposal are to refine and extend our structural studies on a new structural motif we have recently discovered, the "sheared GA-bracketed unpaired G stack". Repeats of the human centromere pentameric DNA sequence TGGAA form stable duplexes with themselves in which "self-complementary" [GGA]2 motifs are separated by an AT and a TA Watson-Crick pair. The (GGA]2 motif consists of sheared GA and AG pairs which bracket two unpaired but costacked (intercalated) guanosines, to form a GGGG stack. The repeated (TGGAA)n sequence occurs at chromosome centromeres and is likely to be important in the separation of chromatids at mitosis. We wish to investigate the ability of residues other than guanosine to stack in the sheared G:A-A:G sandwich, and to study the effect of changing the flanking TA and AT pairs on the structure and stability of the internal [GNA]2 motifs in repeated pentamer sequences. We will also study the ability of the four GNA sequences to adopt sheared unpaired stack [(GNA)n]2 structures when placed immediately adjacent to each other in tandem arrays, i.e. without the intervening AT and TA Watson-Crick pair's The results will be of importance concerning the mechanism of repeat expansion in the triplet-repeat diseases muscular dystrophy, muscular atrophy, and Huntington's disease - all of which appear to be (GCA)n repeats. We will also study the (GCG)n repeats found in Fragile X infant mental retardation. The structure and stability of [GGA]2 motifs, with and without additional looped out residues, will also be investigated in short RNA "internal loops", where they may be implicated in ribozyme function, retroviral recognition and retroviral dimerization. Several purine-rich DNA and RNA hairpins that we expect emerge from our surveys will also be studied by high-resolution NMR at 750 MHz.