DNA elements important for CAG•CTG repeat thresholds in Saccharomyces cerevisiae
DNA elements important for CAG•CTG repeat thresholds in Saccharomyces cerevisiae
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DOI：
10.1093/nar/gkh292
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发表时间：
2004-02-01
影响因子：
14.9
通讯作者：
Lahue, RS
中科院分区：
文献类型：
--
作者：
Dixon, MJ;Lahue, RS
三核苷酸重复序列（TNR）的不稳定性是人们感兴趣的，因为它在人类疾病如亨廷顿病中起着重要作用，并且具有独特的遗传特征。TNR不稳定性的一个显著特征是阈值，其定义为赋予频繁突变的最小重复长度。虽然阈值是很好地建立，致病突变的重要风险决定因素，其机制分析已被推迟缺乏适当的易于处理的实验系统。在这项研究中，我们首次直接比较了三个DNA元素--TNR序列、纯度和侧翼序列--所有这些都在文献中被认为对阈值有贡献。在酵母模型系统中，我们发现CAG重复需要比CTG大片更长的阈值来收缩，这表明滞后的模板重复序列有助于确定阈值。相反，CTG运行中的ATG中断不会通过阈值机制抑制收缩，而是通过改变形成发夹中间体的可能性。富含GC的侧翼序列的存在，类似于在某些亨廷顿病患者中发现的单倍型，并没有可检测地改变冈崎片段CTG束的扩增，表明该侧翼序列对阈值没有作用。这些结果有助于更好地定义TNR阈值描绘序列元件，调节不稳定性。
Trinucleotide repeat (TNR) instability is of interest because of its central role in human diseases such as Huntington's and its unique genetic features. One distinctive characteristic of TNR instability is a threshold, defined as a minimal repeat length that confers frequent mutations. While thresholds are well established, important risk determinants for disease-causing mutations, their mechanistic analysis has been delayed by the lack of suitably tractable experimental systems. In this study, we directly compared for the first time three DNA elements-TNR sequence, purity and flanking sequence-all of which are suggested in the literature to contribute to thresholds. In a yeast model system, we find that CAG repeats require a substantially longer threshold to contract than CTG tracts, indicating that the lagging template repeat sequence helps determine the threshold. In contrast, ATG interruptions within a CTG run do not inhibit contractions via a threshold mechanism, but by altering the likelihood of forming a hairpin intermediate. The presence of a GC-rich flanking sequence, similar to a haplotype found in some Huntington's patients, does not detectably alter expansions of Okazaki fragment CTG tracts, suggesting no role for this flanking sequence on thresholds. Together these results help better define TNR thresholds by delineating sequence elements that modulate instability.