Molecular and Cell Biology, University of California, Berkeley, CA 94720-3200, USA.
Mol Cell Biol. 2011 Feb;31(4):736-43. doi: 10.1128/MCB.01033-10. Epub 2010 Dec 13.
Telomerase promotes telomere maintenance by copying a template within its integral RNA subunit to elongate chromosome ends with new telomeric repeats. Motifs have been defined within the telomerase RNA that contribute to mature RNA accumulation, holoenzyme catalytic activity, or enzyme recruitment to telomeres. Here, we describe a motif of human telomerase RNA (hTR), not previously characterized in a cellular context, comprised of several guanosine tracts near the RNA 5' end. These guanosine tracts together are recognized by the DEXH box RNA helicase DHX36. The helicase domain of DHX36 does not mediate hTR binding; instead, hTR interacts with the N-terminal accessory domain of DHX36 known to bind specifically to the parallel-strand G-quadruplex substrates resolved by the helicase domain. The steady-state level of DHX36-hTR interaction is low, but hTR guanosine tract substitutions substantially reduce mature hTR accumulation and thereby reduce telomere maintenance. These findings suggest that G-quadruplex formation in the hTR precursor improves the escape of immature RNP from degradation, but subsequently the G-quadruplex may be resolved in favor of a longer terminal stem. We conclude that G-quadruplex formation within hTR can stimulate telomerase-mediated telomere maintenance.
端粒酶通过复制其完整 RNA 亚基内的模板来促进端粒的维持，从而用新的端粒重复序列延长染色体末端。已经在端粒酶 RNA 中定义了一些基序，这些基序有助于成熟 RNA 的积累、全酶催化活性或酶向端粒的募集。在这里，我们描述了一个以前在细胞环境中没有被表征的人类端粒酶 RNA（hTR）基序，该基序由 RNA 5'端附近的几个鸟苷tract 组成。这些鸟苷tract 一起被 DEXH 框 RNA 解旋酶 DHX36 识别。DHX36 的解旋酶结构域不介导 hTR 结合；相反，hTR 与 DHX36 的 N 端辅助结构域相互作用，该结构域已知特异性结合解旋酶结构域解析的平行链 G-四链体底物。DHX36-hTR 相互作用的稳态水平较低，但 hTR 鸟苷 tract 取代会大大减少成熟 hTR 的积累，从而降低端粒的维持。这些发现表明，hTR 前体中 G-四链体的形成可以提高不成熟 RNP 逃避降解的能力，但随后 G-四链体可能会被解析，形成更长的末端茎。我们得出结论，hTR 内的 G-四链体形成可以刺激端粒酶介导的端粒维持。
