Do not CROSSlink with DNA damage tolerance

The DNA Damage Tolerance (DDT) system enables a continuation of DNA synthesis in the presence of a plethora of DNA lesions. The most studied mode of DDT is Translesion synthesis (TLS) which takes advantage of specialized damage-tolerant TLS polymerases to enable a direct bypass of a replication impediment. TLS provides an essential repair intermediate step within the Fanconi anemia (FA) repair pathway. The FA pathway resolves toxic DNA lesions i.e., interstrand crosslinks (ICLs). Regarding TLS steps opposite an unhooked ICL, PCNA-Ub as well as REV1 have been implicated. In this thesis, using genetically well-defined mouse models as well as cell lines, we identified site-specific ubiquitination of PCNA at lysine 164 (PCNA-Ub) but not REV1 as key in enabling effective ICL repair. Furthermore, the TLS POLK was identified critical to ICL repair. These results were enabled by generating yet another mouse model, the Fancg-ko mouse model and performing various characterization studies in vivo as well as in vitro. Additionally, we uncovered a novel role of PCNA-Ub in preventing mismatch repair (MMR) factors from getting involved in ICL repair. Furthermore, a global DDT defect had impact on the mutational landscape by causing large genomic deletions. Lastly, we propose the refurbishment of an FDA-approved drug for FA-HNSCC patients. We discuss these results in the context of our current understanding of these fields, the discrepancies, the questions that remain unanswered and how our results provide a step forward to understanding the complexities of ICL repair at multiple steps.