Del Mundo Imee Marie A, Zewail-Foote Maha, Kerwin Sean M, Vasquez Karen M
Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Dell Pediatric Research Institute, 1400 Barbara Jordan Blvd. Austin, TX 78723, USA.
Department of Chemistry and Biochemistry, Southwestern University, 1001 E University Ave, Georgetown, TX 78626, USA.
Nucleic Acids Res. 2017 May 5;45(8):4929-4943. doi: 10.1093/nar/gkx100.
Mutation 'hotspot' regions in the genome are susceptible to genetic instability, implicating them in diseases. These hotspots are not random and often co-localize with DNA sequences potentially capable of adopting alternative DNA structures (non-B DNA, e.g. H-DNA and G4-DNA), which have been identified as endogenous sources of genomic instability. There are regions that contain overlapping sequences that may form more than one non-B DNA structure. The extent to which one structure impacts the formation/stability of another, within the sequence, is not fully understood. To address this issue, we investigated the folding preferences of oligonucleotides from a chromosomal breakpoint hotspot in the human c-MYC oncogene containing both potential G4-forming and H-DNA-forming elements. We characterized the structures formed in the presence of G4-DNA-stabilizing K+ ions or H-DNA-stabilizing Mg2+ ions using multiple techniques. We found that under conditions favorable for H-DNA formation, a stable intramolecular triplex DNA structure predominated; whereas, under K+-rich, G4-DNA-forming conditions, a plurality of unfolded and folded species were present. Thus, within a limited region containing sequences with the potential to adopt multiple structures, only one structure predominates under a given condition. The predominance of H-DNA implicates this structure in the instability associated with the human c-MYC oncogene.
基因组中的突变“热点”区域易受遗传不稳定性影响，这表明它们与疾病有关。这些热点并非随机分布，且常常与可能能够形成替代DNA结构（非B型DNA，如H-DNA和G4-DNA）的DNA序列共定位，这些结构已被确定为基因组不稳定性的内源性来源。有些区域包含重叠序列，可能形成不止一种非B型DNA结构。序列内一种结构对另一种结构的形成/稳定性的影响程度尚未完全了解。为了解决这个问题，我们研究了来自人类c-MYC癌基因中一个染色体断裂热点的寡核苷酸的折叠偏好，该热点同时包含潜在的G4形成元件和H-DNA形成元件。我们使用多种技术表征了在存在G4-DNA稳定离子K+或H-DNA稳定离子Mg2+的情况下形成的结构。我们发现，在有利于H-DNA形成的条件下，一种稳定的分子内三链DNA结构占主导；而在富含K+、有利于G4-DNA形成的条件下，则存在多种未折叠和折叠的物种。因此，在一个有限的区域内，包含有可能形成多种结构的序列，在给定条件下只有一种结构占主导。H-DNA的主导地位表明这种结构与人类c-MYC癌基因相关的不稳定性有关。
