RecPAIR · Genetic landscape of the homology search

The integrity of genetic information is central to life, yet the DNA is vulnerable to damage from internal and external sources. Incorrect repair of DNA damage drives mutagenesis, loss of genetic information, ageing, and cancer. Double strand DNA breaks (DSBs) are perhaps the most threatening DNA lesions, where the integrity of both strands of the DNA duplex is interrupted at the same position. In E. coli, faithful repair of DSBs is possible only through the homologous recombination (HR) pathway which uses replicated chromosome as a template to recover the information. At the center of HR lies an elusive search process, during which broken strand localises and pairs with the repair template.I will use a combination of CRISPR/dCas9 screening and in-situ genotyping of pooled library of strains to characterise the genetic landscape controlling the homology search. First, I will develop a low probability DSB induction method, to limit the DSB-formation to only a single chromosome per cell. Next, I will design and implement a whole-genome CRISPRi screen coupled to high-throughput sequencing and map the genes involved specifically in the homology directed repair of DSBs. The knowledge of the recombination-specific genes will allow to create a refined, high-quality phenotypic screen. In this screen the whole chromosome dynamics will be monitored and defects in the DNA movements will be characterised for each tested target with a microfluidic-based fluorescent microscopy. Each phenotype will be linked to a specific gene using the state-of-the-art in-situ phenotyping approach called DuMPLING. The functional characterisation of recombination genes will allow to conclude a molecular model of the search process in vivo.