Abstract
Translesion polymerase eta (polη) was characterized for its ability to replicate ultraviolet-induced DNA lesions that stall replicative polymerases, a process promoted by Rad18-dependent PCNA mono-ubiquitination. Recent findings have shown that polη also acts at intrinsically difficult to replicate sequences. However, the molecular mechanisms that regulate its access to these loci remain elusive. Here, we uncover that polη travels with replication forks during unchallenged S phase and this requires its SUMOylation on K163. Abrogation of polη SUMOylation results in replication defects in response to mild replication stress, leading to chromosome fragments in mitosis and damage transmission to daughter cells. Rad18 plays a pivotal role, independently of its ubiquitin ligase activity, acting as a molecular bridge between polη and the PIAS1 SUMO ligase to promote polη SUMOylation. Our results provide the first evidence that SUMOylation represents a new way to target polη to replication forks, independent of the Rad18-mediated PCNA ubiquitination, thereby preventing under-replicated DNA.
Highlights
Translesion polymerase eta was characterized for its ability to replicate ultravioletinduced DNA lesions that stall replicative polymerases, a process promoted by Rad18-dependent PCNA mono-ubiquitination
We show that, unexpectedly, polZ travels with replication forks during unperturbed S phase and that this relies on SUMOylation of the translesion synthesis (TLS) polymerase on lysine K163
PolZ was retrieved in the sample harvested immediately after the pulse but lost in the thymidine-chased sample (Fig. 1b). This behaviour is similar to the one of known replisome components, PCNA and the catalytic subunit of the replicative pold (p125), demonstrating that endogenous polZ travels with replication forks during unperturbed S phase
Summary
Translesion polymerase eta (polZ) was characterized for its ability to replicate ultravioletinduced DNA lesions that stall replicative polymerases, a process promoted by Rad18-dependent PCNA mono-ubiquitination. A new function of polZ at intrinsically difficult to replicate DNA loci was proposed in human cells[14,15] Paragons of these loci are the common fragile sites (CFSs), which are DNA regions exquisitely prone to breakage upon mild replication stress, for instance when replicative polymerases are slowed down by a low dose of aphidicolin (APH). We show that, unexpectedly, polZ travels with replication forks during unperturbed S phase and that this relies on SUMOylation of the TLS polymerase on lysine K163 Abrogation of this post-translational modification (PTM) mimics the phenotype of polZ-deficient cells in response to low doses of APH, whereas it has a marginal impact after ultraviolet radiation. These data unravel a new way to recruit polZ to replication forks, especially relevant during lesion-independent replication stress
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