Adding synthetic nucleotides to DNA increases the linear information density of DNA molecules. Here we report that it also can increase the diversity of their three-dimensional folds. Specifically, an additional nucleotide (dZ, with a 5-nitro-6-aminopyridone nucleobase), placed at twelve sites in a 23-nucleotides-long DNA strand, creates a fairly stable unimolecular structure (that is, the folded Z-motif, or fZ-motif) that melts at 66.5 °C at pH 8.5. Spectroscopic, gel and two-dimensional NMR analyses show that the folded Z-motif is held together by six reverse skinny dZ⁻:dZ base pairs, analogous to the crystal structure of the free heterocycle. Fluorescence tagging shows that the dZ⁻:dZ pairs join parallel strands in a four-stranded compact down–up–down–up fold. These have two possible structures: one with intercalated dZ⁻:dZ base pairs, the second without intercalation. The intercalated structure would resemble the i-motif formed by dC:dC⁺-reversed pairing at pH ≤ 6.5. This fZ-motif may therefore help DNA form compact structures needed for binding and catalysis.

在 DNA 中添加合成核苷酸可增加 DNA 分子的线性信息密度。在这里，我们报告说，它还可以增加其三维褶皱的多样性。具体来说，将一个额外的核苷酸（dZ，带有 5-硝基-6-氨基吡啶酮核碱基）放置在 23 个核苷酸长的 DNA 链的 12 个位点上，创建一个相当稳定的单分子结构（即折叠的 Z 基序，或 fZ-基序），熔点为 66.5 °C，pH 8.5。光谱、凝胶和二维 NMR 分析表明，折叠的 Z 基序由六个反向瘦 dZ ⁻ :dZ 碱基对结合在一起，类似于自由杂环的晶体结构。荧光标记显示 dZ ⁻ :dZ 对以四链紧凑的下-上-下-上折叠方式连接平行链。它们有两种可能的结构：一种具有插入的 dZ ⁻ :dZ 碱基对，第二种没有插入。插层结构类似于在 pH ≤ 6.5 时由 dC:dC ⁺ 反向配对形成的 i-基序。因此，这种 fZ 基序可能有助于 DNA 形成结合和催化所需的紧凑结构。