CONICET | Buscador de Institutos y Recursos Humanos

Exposure of cells to genotoxic stimuli causes replication fork stalling at DNA lesions which might lead to fork collapse and subsequent cell death. To preserve viability, cells activate tolerance mechanisms to replicate across damaged DNA. The main known mechanism underlying UVC tolerance is Translesion DNA Synthesis (TLS), with polymerase eta as one of its key players. Template Switching (TS) is another DNA tolerance pathway involving at least some of the classic homologous recombination factors. In fact, TS relies on recombinogenic protein such as Rad51 and Rad 54 to facilitate the search of alternative undamaged template for lesion bypass. The relative contribution of TLS and TS to DNA damage tolerance after UV irradiation is poorly explored. By using the DNA fiber assay herein we show that both TLS and TS facilitate replication fork elongation after UV with apparently no overlapping functions. Intriguingly, the contribution of Rad51 to fork elongation after UV irradiation exceeds that of TS. Rad51 prevents a massive UV-triggered and mirin sensitive degradation of newly synthesized DNA. DNA degradation in the absence of Rad51 was limited to nucleotides incorporated before UV irradiation and was independent of PAR, a factor required for fork reversal. Conversely, DNA elongation after UV irradiation was largely affected by PAR inhibition, but this effect was not associated with any Rad51 function. Our work demonstrates that DNA replication after UV relies on a plethora of processes including TLS, TS and the protection of fork integrity by a non-recombinogenic function of Rad51. Importantly, this role of Rad51 is required for cell survival after UV irradiation and might therefore be central for the cellular response to the accumulation of bulky adducts.