Ctf18-dependent localization of interstitial telomeric sequence to nuclear pore complexes prevents chromosome fragility

Abstract

Nuclear pore complexes (NPCs) have emerged as hubs in the spatial regulation of DNA damage repair, including restart of stalled replication forks. Here, we used chromatin endogenous cleavage to show that interstitial telomeric sequence (ITS) and natural telomeres interact with the NPCs during their replication in telomerase-positive cells This localization is triggered by replication fork pausing induced by tight Rap1 binding to ITS and requires the alternative PCNA loader Ctf18, consistent with its interaction with the nucleoporin Nup170 in S phase. Mrc1, acting in the same epistatic group with Ctf18 in sister chromatid cohesion establishment during DNA replication, and the cohesin loader Scc2 contribute to localization to NPCs suggesting cohesin involvement downstream of Ctf18. Pol2 SUMOylation by the SUMO ligase Mms21 also participates in this process in epistasis with Scc2. We propose that SUMOylation and establishment of sister chromatid cohesion behind stalled forks mediate Ctf18-dependent localization to NPCs. Chromosome fragility assays show that the NPC environment protects the forks paused at ITS from homologous recombination-induced breakage, thus favoring their error-free restart.