Research
Replication intermediates visualised by Transmission Electron Microscopy (TEM). Upon DNA synthesis problems replication forks can stall. Exonucleolytic resection of nascent DNA strands by Polɛ can generate single stranded DNA gaps (gapped forks) which destabilise replication forks priming genome instability. Checkpoint kinases curb exnonucleolisys by Polɛ protecting fork integrity.
04 May 2021
The mechanism by which the checkpoint-mediated DNA polymerase ɛ exonuclease activity curbing preserves the integrity of replication forks unveiled
A new work led by Dr. Rodrigo Bermejo and his group at Centro de Investigaciones Biológicas Margarita Salas and published in Molecular Cell reveals the mechanism by which replication checkpoint kinases shift the Polɛ leading strand polymerase to an exonucleasesafe mode preventing fork resection and collapse.
DNA polymerase ɛ (Polɛ) is one of the two major replicases which carry out the replication of the nuclear genome. Polɛ carries out high-fidelity DNA leading strand synthesis thanks to its exonuclease activity which corrects errors and avoids mutations. However, Polɛ polymerase and exonuclease activities are balanced, because of the partitioning of nascent DNA strands between catalytic sites, so that net resection occurs when synthesis is impaired.
In vivo, DNA synthesis stalling activates replication checkpoint kinases, which act to preserve the functional integrity of replication forks. The study, which results from an international collaboration, has shown that the checkpoint-dependent phosphorylation of a key residue on the Polɛ catalytic core by these kinases curbs nascent strand partitioning between active sites otherwise imbalanced towards exonucleolysis owing to synthesis stalling.
The findings presented in this work by Pellicano et al. reveal that checkpoint kinases switch Polɛ to an exonuclease-safe mode preventing nascent strand resection and stabilizing stalled replication forks. Additionally, elective partitioning suppression has implications for the diverse Polɛ roles in genome integrity maintenance.
Reference: Checkpoint-mediated DNA polymerase ɛ exonuclease activity curbing counteracts resection-driven fork collapse. Grazia Pellicano, Mohammed Al Mamun, Dolores Jurado-Santiago, Sara Villa-Hernández, Xingyu Yin, Michele Giannattasio, Michael C. Lanz, Marcus B. Smolka, Joseph Yeeles, Katsuhiko Shirahige, Miguel García-Díaz, Rodrigo Bermejo. Molecular Cell (2021) https://doi.org/10.1016/j.molcel.2021.04.006