Telomerase adds telomeric repeats at chromosome ends to compensate for the telomere loss that is caused by incomplete genome end replication¹. In humans, telomerase is upregulated during embryogenesis and in cancers, and mutations that compromise the function of telomerase result in disease². A previous structure of human telomerase at a resolution of 8 Å revealed a vertebrate-specific composition and architecture³, comprising a catalytic core that is flexibly tethered to an H and ACA (hereafter, H/ACA) box ribonucleoprotein (RNP) lobe by telomerase RNA. High-resolution structural information is necessary to develop treatments that can effectively modulate telomerase activity as a therapeutic approach against cancers and disease. Here we used cryo-electron microscopy to determine the structure of human telomerase holoenzyme bound to telomeric DNA at sub-4 Å resolution, which reveals crucial DNA- and RNA-binding interfaces in the active site of telomerase as well as the locations of mutations that alter telomerase activity. We identified a histone H2A–H2B dimer within the holoenzyme that was bound to an essential telomerase RNA motif, which suggests a role for histones in the folding and function of telomerase RNA. Furthermore, this structure of a eukaryotic H/ACA RNP reveals the molecular recognition of conserved RNA and protein motifs, as well as interactions that are crucial for understanding the molecular pathology of many mutations that cause disease. Our findings provide the structural details of the assembly and active site of human telomerase, which paves the way for the development of therapeutic agents that target this enzyme.

端粒酶在染色体末端添加端粒重复序列，以补偿由不完整的基因组末端复制¹引起的端粒丢失。在人类中，端粒酶在胚胎发生过程和癌症中被上调，而损害端粒酶功能的突变会导致疾病²。先前分辨率为 8 Å 的人类端粒酶结构揭示了脊椎动物特有的成分和结构³，包含一个催化核心，该核心通过端粒酶 RNA 灵活地连接到 H 和 ACA（以下简称 H/ACA）盒核糖核蛋白 (RNP) 叶。高分辨率的结构信息对于开发能够有效调节端粒酶活性的治疗方法是必要的，作为一种治疗癌症和疾病的方法。在这里，我们使用低温电子显微镜来确定与端粒 DNA 结合的人类端粒酶全酶的结构，分辨率为 4 Å，这揭示了端粒酶活性位点中关键的 DNA 和 RNA 结合界面以及突变的位置。改变端粒酶活性。我们在全酶中发现了一个组蛋白 H2A-H2B 二聚体，它与一个必需的端粒酶 RNA 基序结合，这表明组蛋白在端粒酶 RNA 的折叠和功能中发挥作用。此外，真核 H/ACA RNP 的这种结构揭示了对保守 RNA 和蛋白质基序的分子识别，以及对于理解许多引起疾病的突变的分子病理学至关重要的相互作用。我们的研究结果提供了人类端粒酶组装和活性位点的结构细节，这为开发针对这种酶的治疗剂铺平了道路。