Soutenance de thèse : Deciphering the crosstalk between the base excision and nucleotide excision repair pathways in D. radiodurans

Par Mohammad Rida Hayek (IBS/Groupe Imagerie Intégrée de la Réponse au Stress & SYMMES)

The radiation resistant bacterium, Deinococcus radiodurans, is known to possess a relatively conserved DNA repair machinery, and yet, it exhibits an outstanding DNA repair efficiency. We hypothesized that a possible synergy between different DNA repair pathways might explain this remarkable repair capacity. To test this hypothesis, my PhD thesis aimed at investigating a possible crosstalk between the nucleotide excision repair (NER) and the base excision repair (BER) pathways of D. radiodurans, which together are responsible for the eradication of DNA lesions occurring at the nucleobase level. To test that, we used a bacterial two-hybrid system to probe interactions among NER factors and between NER and BER factors. Several direct NER-NER and NER-BER interactions were identified and subsequently validated by pull-down assays, native-gel electrophoresis and biophysically characterized by Biolayer interferometry (BLI). To understand whether these newly identified interactions have a consequence on the DNA repair activity, we started to explore a functional interplay by combining the NER machinery and Fpg on various DNA substrates. We showed that the NER competes Fpg to bind 8-oxo-G, and further processes its product, which gave insight into the presence of functional interplay between these two repair pathways. Based on our findings, we proposed UvrA1 as NER hub protein and UvrA2 as a crosstalk mediator between the NER and BER pathways. Together, these studies have provided a strong evidence on the presence of a complex interaction between two important repair pathways in D. radiodurans, shedding insight into one of its possible mechanisms to have an extraordinary repair efficiency using a conserved repair machinery.