UNUSUAL NUCLEIC ACID STRUCTURES IN BIOLOGY

这项提议的目标是完善和扩展我们的结构 关于我们最近发现的一个新的结构基序的研究 “已剪切GA-括号无对G堆栈”。人类着丝粒的重复 五聚体DNA序列TGGAA与自身形成稳定的双链 哪个[GGA]2基序由AT和TA分隔 沃森-克里克组合。(GGA]2基序由剪切的GA和AG对组成 该括号包括两个未配对但共堆叠(插层)的鸟苷，以 形成一个GGGG堆栈。重复的(TGGAA)n序列出现在染色体上 着丝粒，在染色单体的分离中很可能是重要的 在有丝分裂时。 我们希望研究鸟苷以外的残基对 在剪切的G：A-A：G夹层中叠加，并研究改变的效果 侧翼TA和AT对结构和稳定性的影响 重复的五聚体序列中的内部[GNA]2基序。我们还将研究 四个GNA序列采用剪切型非配对堆叠的能力 [(GNA)n]2个结构在 串联阵列，即没有介入的AT和TA Watson-Crick对 这一结果将对重复的机制具有重要意义 三重复发性肌营养不良症的扩张性 萎缩和亨廷顿病--所有这些似乎都是(GCA)n 重复着。我们还将研究在脆性X婴儿中发现的(GCG)n重复序列 精神发育迟滞。 [GGA]2基序的结构和稳定性 循环出来的残基，也将在短RNA中进行调查 “环”，其中它们可能与核酶功能有关，逆转录病毒 识别和逆转录病毒二聚体。几种富含嘌呤的DNA和RNA 我们预计从我们的调查中出现的发夹也将由 750 MHz的高分辨率核磁共振。

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.