CST-polymerase α-primase solves a second telomere end-replication problem

• 成果类型: Article
• 署名作者: Takai, Hiroyuki; Aria, Valentina; Borges, Pamela; Yeeles, Joseph T. P.; de Lange, Titia
• 署名单位: Rockefeller University; UK Research & Innovation (UKRI); Medical Research Council UK (MRC); MRC Laboratory Molecular Biology
• 刊物名称: Nature
• ISSN/ISSBN: 0028-5838
• DOI: 10.1038/s41586-024-07137-1
• 发表日期: 2024-03-21
• 关键词: maintenance component 1; fill-in; mammalian telomeres; accessory protein; chromosome ends; dna-replication; reveals; complex

摘要

Telomerase adds G-rich telomeric repeats to the 3 ' ends of telomeres1, counteracting telomere shortening caused by loss of telomeric 3 ' overhangs during leading-strand DNA synthesis ('the end-replication problem'2). Here we report a second end-replication problem that originates from the incomplete duplication of the C-rich telomeric repeat strand (C-strand) by lagging-strand DNA synthesis. This problem is resolved by fill-in synthesis mediated by polymerase alpha-primase bound to Ctc1-Stn1-Ten1 (CST-Pol alpha-primase). In vitro, priming for lagging-strand DNA replication does not occur on the 3 ' overhang and lagging-strand synthesis stops in a zone of approximately 150 nucleotides (nt) more than 26 nt from the end of the template. Consistent with the in vitro data, lagging-end telomeres of cells lacking CST-Pol alpha-primase lost 50-60 nt of telomeric CCCTAA repeats per population doubling. The C-strands of leading-end telomeres shortened by around 100 nt per population doubling, reflecting the generation of 3 ' overhangs through resection. The measured overall C-strand shortening in the absence of CST-Pol alpha-primase fill-in is consistent with the combined effects of incomplete lagging-strand synthesis and 5 ' resection at the leading ends. We conclude that canonical DNA replication creates two telomere end-replication problems that require telomerase to maintain the G-rich strand and CST-Pol alpha-primase to maintain the C-strand. Incomplete duplication of the C-rich telomeric repeat strand by lagging-strand DNA synthesis is counteracted by DNA synthesis mediated by CST-polymerase alpha-primase.