The Multiple Roles of Ubiquitylation in Regulating Challenged DNA Replication.

DNA replication is essential for the propagation of life and the development of complex organisms. However, replication is a risky process as it can lead to mutations and chromosomal alterations. Conditions challenging DNA synthesis by replicative polymerases or DNA helix unwinding, generally termed as replication stress, can halt replication fork progression. Stalled replication forks are unstable, and mechanisms exist to protect their integrity, which promote an efficient restart of DNA synthesis and counteract fork collapse characterized by the accumulation of DNA lesions and mutagenic events. DNA replication is a highly regulated process, and several mechanisms control replication timing and integrity both during unperturbed cell cycles and in response to replication stress. Work over the last two decades has revealed that key steps of DNA replication are controlled by conjugation of the small peptide ubiquitin. While ubiquitylation was traditionally linked to protein degradation, the complexity and flexibility of the ubiquitin system in regulating protein function have recently emerged. Here we review the multiple roles exerted by ubiquitin-conjugating enzymes and ubiquitin-specific proteases, as well as readers of ubiquitin chains, in the control of eukaryotic DNA replication and replication-coupled DNA damage tolerance and repair.