Mechanisms for Maintaining Eukaryotic Replisome Progression in the Presence of DNA Damage

Abstract

The eukaryotic replisome coordinates template unwinding and nascent-strand synthesis to drive DNA replication fork progression and complete efficient genome duplication. During its advancement along the parental template, each replisome may encounter an array of obstacles including damaged and structured DNA that impede its progression and threaten genome stability. A number of mechanisms exist to permit replisomes to overcome such obstacles, maintain their progression, and prevent fork collapse. A combination of recent advances in structural, biochemical, and single-molecule approaches have illuminated the architecture of the replisome during unperturbed replication, rationalised the impact of impediments to fork progression, and enhanced our understanding of DNA damage tolerance mechanisms and their regulation. This review focusses on these studies to provide an updated overview of the mechanisms that support replisomes to maintain their progression on an imperfect template.

Post-Translational Modifications of PCNA: Guiding for the Best DNA Damage Tolerance Choice

“…Nevertheless, template unwinding and lagging-strand synthesis continue, generating stretches of RPA-coated ssDNA on the leading strand. Switching replicative polymerases allows for the rapid continuation of replication after uncoupling, by ensuring high-fidelity replicative polymerase DNA synthesis on the leading strand, to elude mutagenic DDT processes and checkpoint activation [ 116 ] ( Figure 1 ). Once DNA synthesis is finished, the complex regulation of PCNA unloading is tightly controlled by different processes [ 64 , 94 , 98 , 103 , 104 , 105 , 106 , 107 , 109 , 117 ]; then, PCNA clamps multiple enzymes necessary for chromosome assembly [ 4 , 5 , 6 ], sister chromatid cohesion [ 7 , 8 , 9 ] or gene expression [ 15 , 16 ].…”

“…Compared to replicative polymerases, TLS polymerases exhibit intrinsic structural features that couple with their role in synthesizing damaged DNA [ 116 ]. In this sense, the Y-family DNA polymerases hold an especially flexible conformation at active sites to provide room to tolerate a variety of bulky, damaged template bases [ 158 , 159 ].…”

“…In this model, Polδ dissociates from PCNA and DNA to permit TLS. Rev1 interacts with PCNA through the BRCT domain, and through PIP-like motifs with other Y-family polymerases [ 78 ] or with the Rev7 subunit of Polζ [ 116 , 188 ]. Accordingly, numerous studies support a non-catalytic role of Rev1 in the recruitment of other TLS polymerases [ 189 , 190 , 191 , 192 ].…”

“…Accordingly, numerous studies support a non-catalytic role of Rev1 in the recruitment of other TLS polymerases [ 189 , 190 , 191 , 192 ]. Single-molecule studies revealed that both mechanisms, “tool belt” and Rev1 bridges, are able to dynamically interchange without dissociation [ 116 , 147 ]. Furthermore, their relative contribution is likely to be lesion-specific (for more information on the subject, see [ 142 ]).…”

Mre11 exonuclease activity promotes irreversible mitotic progression under replication stress

“…The fork stabilization system ensures that replisomes are stably maintained at stalled forks (or maybe reversed forks) under replication stress, which enables replication restart without de novo assembly of replisomes in the S-phase ( Bellelli & Boulton, 2021 ; Guilliam, 2021 ). However, these stabilized replisomes are disassembled by increasing mitotic CDK activity that leads to cell cycle progression into mitosis ( Hashimoto & Tanaka, 2018 ).…”