Molecular Biophysics Unit, Indian Institute of Science, Bengaluru, 560012, India.
NMR Research Centre, Indian Institute of Science, Bengaluru, 560012, India.
Nucleic Acids Res. 2020 May 7;48(8):4492-4506. doi: 10.1093/nar/gkaa134.
The telomere repeats containing RNA (TERRA) is transcribed from the C-rich strand of telomere DNA and comprises of UUAGGG nucleotides repeats in humans. The TERRA RNA repeats can exist in single stranded, RNA-DNA hybrid and G-quadruplex forms in the cell. Interaction of TERRA RNA with hnRNPA1 has been proposed to play critical roles in maintenance of telomere DNA. hnRNPA1 contains an N-terminal UP1 domain followed by an RGG-box containing C-terminal region. RGG-motifs are emerging as key protein motifs that recognize the higher order nucleic acid structures as well as are known to promote liquid-liquid phase separation of proteins. In this study, we have shown that the RGG-box of hnRNPA1 specifically recognizes the TERRA RNA G-quadruplexes that have loops in their topology, whereas it does not interact with the single-stranded RNA. Our results show that the N-terminal UP1 domain in the presence of the RGG-box destabilizes the loop containing TERRA RNA G-quadruplex efficiently compared to the RNA G-quadruplex that lacks loops, suggesting that unfolding of G-quadruplex structures by UP1 is structure dependent. Furthermore, we have compared the telomere DNA and TERRA RNA G-quadruplex binding by the RGG-box of hnRNPA1 and discussed its implications in telomere DNA maintenance.
端粒重复含 RNA（TERRA）由端粒 DNA 的 C 丰富链转录而成，人类的 TERRA RNA 重复序列由 UUAGGG 核苷酸重复组成。TERRA RNA 可以在细胞中以单链、RNA-DNA 杂交和 G-四链体的形式存在。TERRA RNA 与 hnRNPA1 的相互作用被认为在端粒 DNA 的维持中发挥关键作用。hnRNPA1 含有一个 N 端的 UP1 结构域，其后是一个含有 C 端区域的 RGG 盒。RGG 基序作为识别高级核酸结构的关键蛋白基序而出现，并且已知可促进蛋白质的液-液相分离。在这项研究中，我们表明 hnRNPA1 的 RGG 盒特异性识别拓扑结构中具有环的 TERRA RNA G-四链体，而不与单链 RNA 相互作用。我们的结果表明，与缺乏环的 RNA G-四链体相比，RGG 盒存在时，N 端的 UP1 结构域能有效地使含有环的 TERRA RNA G-四链体不稳定，这表明 UP1 通过解折叠 G-四链体结构是结构依赖性的。此外，我们比较了 hnRNPA1 的 RGG 盒对端粒 DNA 和 TERRA RNA G-四链体的结合，并讨论了其对端粒 DNA 维持的影响。
