Modification of PCNA by ISG15 Plays a Crucial Role in Termination of Error-Prone Translesion DNA Synthesis

•In response to UV, mono-ubiquitinated PCNA recruits EFP for its ISGylation•ISGylated PCNA tethers USP10 for its deubiquitination and release of polymerase-η•UBP43 eventually deISGylates PCNA for resumption of normal DNA replication•PCNA ISGylation is crucial for termination of error-prone translesion DNA synthesis

SummaryIn response to DNA damage, PCNA is mono-ubiquitinated and triggers translesion DNA synthesis (TLS) by recruiting polymerase-η. However, it remained unknown how error-prone TLS is turned off after DNA lesion bypass to prevent mutagenesis. Here we showed that ISG15 modification (ISGylation) of PCNA plays a key role in TLS termination. Upon UV irradiation, EFP, an ISG15 E3 ligase, bound to mono-ubiquitinated PCNA and promoted its ISGylation. ISGylated PCNA then tethered USP10 for deubiquitination and in turn the release of polymerase-η from PCNA. Eventually, PCNA was deISGylated by UBP43 for reloading of replicative DNA polymerases and resuming normal DNA replication. However, ISGylation-defective Lys-to-Arg mutations in PCNA or knockdown of any of ISG15, EFP, or USP10 led to persistent recruitment of mono-ubiquitinated PCNA and polymerase-η to nuclear foci, causing an increase in mutation frequency. These findings establish a crucial role of PCNA ISGylation in termination of error-prone TLS for preventing excessive mutagenesis.

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