CONICET | Buscador de Institutos y Recursos Humanos

The accumulation of DNA adducts caused by UV irradiation triggers replication fork stalling, collapse and subsequent cell death. To preserve viability, cells activate the DNA damage tolerance mechanisms, Translesion DNA Synthesis (TLS) by alternative polymerases. The participation of other tolerance options such template switching (TS) in the cellular response to UV irradiation is less clear in mammals. Using the DNA fiber assay we demonstrate that the TLS-pol eta and TS factors such as Rad51 and Rad54 are all necessary for the proper elongation of ongoing forks after UV irradiation. Intriguingly, Rad51, but not Rad54 or pol  is necessary to prevent a massive UV- triggered, mirin-sensitive degradation of DNA. Such nucleolytic degradation affects only the DNA tracks synthesized before but not after UV irradiation. Intriguingly as well, whereas fork degradation was suggested to take place on reversed replication forks this is unlikely the case after UV irradiation. In fact, while we observed detectable fork elongation when PARP, a factor that is central for fork reversal, was inhibited in UV treated samples such effect was not at linked or required for the fork degradation observed in Rad51 depleted background. Finally, while DNA degradation is not evident in the tracks of DNA synthesized after UV irradiation, Rad51 still exerts another function which is the prevention of excessive elongation of DNA after UV irradiation. The multiple alterations in DNA elongation caused by Rad51 depletion triggered long term DNA replication defects and increased cell death. Together, our findings reveal a complex contribution of multiple mechanisms including, but not restricted to TLS and TS to the progression of elongating forks after UV irradiation