Ubiquitin and
ubiquitin-like proteins (Ubls) are now at the center stage of molecular and cell biology because of their diverse functions in many fundamentally important cellular processes. Besides the celebrated role of
ubiquitin in the
26S proteasome-mediated protein degradation pathway, the non-proteolytic functions of
ubiquitin are being uncovered at a fast pace. The prominent examples include membrane trafficking, innate immunity,
kinase signaling,
chromatin dynamics and DNA damage response. Researchers in the area of DNA damage response have witnessed rapid progress within the past decade, largely stimulated by the seminal findings that ubiquitination and SUMOylation of a key DNA replication/repair
protein,
proliferating cell nuclear antigen (
PCNA), controls precisely how eukaryotic cells respond to different types of DNA damage, and how cellular DNA damage repair or tolerance pathways are selected to cope with damage in the
DNA genome. Here, we will review the recent findings on translesion synthesis (TLS) and its regulation by
PCNA ubiquitination in eukaryotes. We will discuss two prevalent models, i.e., the postreplicative gap-filling and the polymerase switch, which have been invoked to account for eukaryotic cells' ability to overcome DNA damage associated replication blockade through TLS. Results from both in vitro reconstitution and from genetic systems will be discussed. We will also summarize the recent findings revealing the crosstalk between two major human DNA damage response pathways (the TLS and the
Fanconi anemia pathways), and the ATR and ATM-independent regulation of
PCNA ubiquitination. Lastly, new methods of preparing ubiquitinated
PCNA will be reviewed. The availability of milligram levels of ubiquitinated
PCNA will help our understanding of the molecular details in eukaryotic TLS.