Marco Fumasoni

DNA damage tolerance (DDT) mechanisms are crucial for genome integrity as they allow efficient bypass of endogenously or exogenously generated lesions. Error-free bypass of lesions is accomplished by a recombination-related mechanism, generally referred to as template switching (TS), that allows the recovery of the damaged information from the sister chromatid. Pioneer studies revealed key enzymatic functions required for error-free DDT and identified sister chromatid junctions (SCJs) as crucial DNA intermediates mediating this process. However, little is known on the temporal window and the chromatin/topological context in which TS takes place. Using S. cerevisiae as a model system, here I investigated the contribution of different replication-related processes to recombination-mediated DDT. We identified sister chromatid cohesion and replication-related repriming/primer processing as novel pathways implicated in TS. Unexpectedly, repriming during replication impinges on sister chromatid cohesion, but these two processes differentially contribute to errorfree DDT. Repriming activities and other processes influencing the size of the ssDNA gap and the availability of the 5 end positively influence error-free DDT both in spontaneous and genotoxic stress conditions. Our results provide evidence that error free DDT is largely a recombination-mediated gap-filling process with different requirements from the recombination mechanism involved in double strand break repair, both in what regards the influence of DNA end processing on the subsequent homology search and strand invasion, and the contribution of the chromatin structural context mediated by sister chromatid cohesion. Our findings suggest that mechanisms promoting damage-bypass via replication-associated SCJ formation affect DDT pathway choice and the establishment of post replicative sister chromatid synapses.