Department of Molecular and Cellular Biology and Genome Center, University of California Davis, Davis, CA, USA.
Integrative Genetics and Genomics Graduate Group, University of California Davis, Davis, CA, USA.
Methods Mol Biol. 2020;2161:209-228. doi: 10.1007/978-1-0716-0680-3_15.
R-loops are three-stranded structures that form during transcription when the nascent RNA hybridizes with the template DNA resulting in a DNA:RNA hybrid and a looped-out single-stranded DNA (ssDNA) strand. These structures are important for normal cellular processes and aberrant R-loop formation has been implicated in a number of pathological outcomes, including certain cancers and neurodegenerative diseases. Mapping R-loops has primarily been performed using DRIP (DNA:RNA immunoprecipitation) based methods that are dependent on the anti-DNA:RNA hybrid S9.6 antibody and short-read sequencing. While DRIP-based methods are robust and report R-loop formation genome-wide, they only do so at the population average level; interrogating R-loop formation at the single molecule level is not feasible with such approaches. Here we present single molecule R-loop footprinting (SMRF-seq), a method that relies on the chemical reactivity of the displaced ssDNA strand to non-denaturing sodium bisulfite and single molecule long-read sequencing as a readout, to characterize R-loops. SMRF-seq can be used independently of S9.6 to generate high resolution, strand-specific, maps of individual R-loops at ultra-deep coverage on kilobases-length DNA fragments.
R 环是转录过程中形成的三链结构,当新生 RNA 与模板 DNA 杂交时,会形成 DNA:RNA 杂交体和一个环出的单链 DNA(ssDNA)链。这些结构对于正常的细胞过程很重要,异常的 R 环形成与许多病理结果有关,包括某些癌症和神经退行性疾病。R 环的作图主要是通过基于 DRIP(DNA:RNA 免疫沉淀)的方法来完成的,这些方法依赖于抗 DNA:RNA 杂交体 S9.6 抗体和短读测序。虽然基于 DRIP 的方法强大且可以全面报告 R 环的形成,但它们只能在群体平均水平上进行;通过这种方法在单分子水平上检测 R 环的形成是不可行的。在这里,我们提出了单分子 R 环足迹(SMRF-seq),这是一种依赖于取代的 ssDNA 链的化学反应性的方法,利用非变性亚硫酸氢钠和单分子长读测序作为读出,来表征 R 环。SMRF-seq 可以独立于 S9.6 使用,在超深覆盖度下在千碱基长度的 DNA 片段上生成高分辨率、链特异性的单个 R 环图谱。