An increasing number of human disorders are attributed to genomic expansions of short tandem repeats (STRs). Secondary DNA structures formed by STRs are believed to play an important role in expansion, while the presence of nucleotide interruptions within the pure repeat sequence is known to delay the onset and progression of disease. We have used two single-molecule fluorescence techniques to analyse the structure and dynamics of DNA three-way junctions (3WJs) containing CAG repeat hairpin slipouts, with and without a single CAA interrupt. For a 3WJ with a (CAG)10 slipout, the CAA interrupt is preferentially located in the hairpin loop, and the branch migration dynamics are 4-fold slower than for the 3WJ with a pure (CAG)10, and 3-fold slower than a 3WJ with a pure (CAG)40 repeat. The (CAG)11 3WJ with CAA interrupt adopts a conformation that places the interrupt in or near the hairpin loop, with similar dynamics to the pure (CAG)10 and (CAG)11 3WJs. We have shown that changing a single nucleotide (G to A) in a pure repeat can have a large impact on 3WJ structure and dynamics, which may be important for the protective role of interrupts in repeat expansion diseases.

中文翻译：

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包含 CAG 重复发夹的 DNA 三向连接中的单个 CAA 中断会导致奇偶校验依赖性捕获


越来越多的人类疾病归因于短串联重复序列（STR）的基因组扩展。人们认为由 STR 形成的二级 DNA 结构在扩增中发挥着重要作用，而纯重复序列中核苷酸中断的存在已知可以延缓疾病的发生和进展。我们使用两种单分子荧光技术来分析包含 CAG 重复发夹滑脱的 DNA 三路连接 (3WJ) 的结构和动态，无论是否存在单个 CAA 中断。对于具有 (CAG)10 滑出的 3WJ，CAA 中断优先位于发夹环中，并且分支迁移动力学比具有纯 (CAG)10 的 3WJ 慢 4 倍，比具有纯 (CAG)10 的 3WJ 慢 3 倍。具有纯 (CAG)40 重复的 3WJ。具有 CAA 中断的 (CAG)11 3WJ 采用将中断置于发夹环路中或发夹环路附近的构造，其动态特性与纯 (CAG)10 和 (CAG)11 3WJ 类似。我们已经证明，改变纯重复中的单个核苷酸（G 到 A）可以对 3WJ 结构和动力学产生很大影响，这对于重复扩展疾病中中断的保护作用可能很重要。