Human genome function is underpinned by the primary storage of genetic information in canonical B-form DNA, with a second layer of DNA structure providing regulatory control. I-motif structures are thought to form in cytosine-rich regions of the genome and to have regulatory functions; however, in vivo evidence for the existence of such structures has so far remained elusive. Here we report the generation and characterization of an antibody fragment (iMab) that recognizes i-motif structures with high selectivity and affinity, enabling the detection of i-motifs in the nuclei of human cells. We demonstrate that the in vivo formation of such structures is cell-cycle and pH dependent. Furthermore, we provide evidence that i-motif structures are formed in regulatory regions of the human genome, including promoters and telomeric regions. Our results support the notion that i-motif structures provide key regulatory roles in the genome.

人类基因组功能的基础是规范B型DNA中遗传信息的主要存储，而第二层DNA结构则提供了调节控制。I-基序结构被认为在基因组中富含胞嘧啶的区域形成并具有调节功能。然而，迄今为止，尚无关于这种结构存在的体内证据。在这里，我们报告的抗体片段（iMab）的生成和表征，以高选择性和亲和力识别i-基序结构，从而能够检测人细胞核中的i-基序。我们证明这种结构的体内形成是细胞周期和pH依赖性的。此外，我们提供的证据表明，i-基序结构是在人类基因组的调控区域中形成的，包括启动子和端粒区域。