G-Quadruplexes are secondary structures that can form in guanine-rich DNA and RNA that have been implicated in regulating multiple biological processes, including transcription. G-Quadruplex-forming sequences are prevalent in promoter regions of proto-oncogenes and DNA repair proteins. HELB is a human helicase involved in DNA replication and repair with 12 runs of three to four guanines in the proximal promoter. This sequence has the potential to form three canonical three-tetrad G-quadruplexes. Our results show that although all three G-quadruplexes can form, a structure containing two noncanonical G-quadruplexes with longer loops containing runs of three to four guanines is the most prevalent. These HELB G-quadruplexes are stable under physiological conditions. In cells, stabilization of the G-quadruplexes results in a decrease in the level of HELB expression, suggesting that the G-quadruplexes in the HELB promoter serve as transcriptional repressors.

中文翻译：

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人DNA解旋酶B的表达受启动子中G-四链体的影响。

G-四链体是可以在富含鸟嘌呤的DNA和RNA中形成的二级结构，已参与调节多种生物过程，包括转录。G-四链体形成序列普遍存在于原癌基因和DNA修复蛋白的启动子区域。HELB是一种人类解旋酶，参与DNA复制和修复，在近端启动子中运行12道3至4个鸟嘌呤。此序列有可能形成三个规范的三重G四联体。我们的结果表明，尽管所有三个G-四链体都可以形成，但最常见的结构是包含两个具有更长环的非规范性G-四链体，该环包含三到四个鸟嘌呤。这些HELBG-四链体在生理条件下是稳定的。在细胞中，G-四链体的稳定导致HELB表达水平的降低，表明HELB启动子中的G-四链体起着转录抑制因子的作用。