The RAD6 DNA Damage Tolerance Pathway Operates Uncoupled from the Replication Fork and Is Functional Beyond S Phase

SummaryDamaged DNA templates provide an obstacle to the replication fork and can cause genome instability. In eukaryotes, tolerance to damaged DNA is mediated largely by the RAD6 pathway involving ubiquitylation of the DNA polymerase processivity factor PCNA. Whereas monoubiquitylation of PCNA mediates error-prone translesion synthesis (TLS), polyubiquitylation triggers an error-free pathway. Both branches of this pathway are believed to occur in S phase in order to ensure replication completion. However, we found that limiting TLS or the error-free pathway to the G2/M phase of the cell-cycle efficiently promote lesion tolerance. Thus, our findings indicate that both branches of the DNA damage tolerance pathway operate effectively after chromosomal replication, outside S phase. We therefore propose that the RAD6 pathway acts on single-stranded gaps left behind newly restarted replication forks.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (132 K)Download as PowerPoint slideHighlights► Error-free and error-prone DNA damage tolerance can function outside S phase ► The RAD6 DNA damage tolerance pathway is independent of the replication fork ► The RAD6 pathway seems to act on single-stranded gaps behind the replication fork