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bioRxiv · 10.1101/2023.10.26.564248

CST--Polymeraseα-primase solves a second telomere end-replication problem

Takai, H.·Aria, V.·Borges, P.·Yeeles, J. T. P.·de Lange, T.
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Abstract

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). We report a second end-replication problem that originates from the incomplete duplication of the C-rich telomeric repeat strand by lagging-strand synthesis. This problem is solved by CST-Polymerase(Pol)-primase fill-in synthesis. In vitro, priming for lagging-strand DNA replication does not occur on the 3 overhang and lagging-strand synthesis stops in an [~]150-nt zone more than 26 nt from the end of the template. Consistent with the in vitro data, lagging-end telomeres of cells lacking CST-Pol-primase lost [~]50-60 nt of CCCTAA repeats per population doubling (PD). The C-strands of leading-end telomeres shortened by [~]100 nt/PD, reflecting the generation of 3 overhangs through resection. The measured overall C-strand shortening in absence of CST-Pol-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-strand and CST-Pol-primase to maintain the C-strand.

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Takai, H., Aria, V., Borges, P., Yeeles, J. T. P., de Lange, T.. 2023-10-26. CST--Polymeraseα-primase solves a second telomere end-replication problem. https://doi.org/10.1101/2023.10.26.564248

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