Chemically ubiquitylated PCNA as a probe for eukaryotic translesion DNA synthesis

The rapid growth in ubiquitin biology requires facile chemical approaches for protein ubiquitylation that can overcome the common problem of low yield faced by the enzymatic reaction catalyzed by ubiquitin ligases. We report a chemical approach for monoubiquitylation and SUMOylation of PCNA through disulfide exchange and intein chemistry. We used the chemically ubiquitylated and SUMOylated PCNAs in studying translesion DNA synthesis and revealed a surprising degree of flexibility of the ubiquitin modification.