Mutations in DNA have large-ranging consequences, from evolution to diseases. Dysfunctions in DNA repair and transcription, and mutagen exposures can increase the rate of mutations. It remains poorly understood how the interplay between these processes influences mutagenesis. Transcription-coupled repair (TCR) lowers mutational rates by preferentially removing lesions from the transcribed strand. Transcription has also an opposite effect by inducing transcription-associated mutagenesis (TAM). Their relative contribution on mutagenesis and the precise mechanisms remain unclear. Our hypothesis is that transcription affects mutational rate by different mechanisms that include TCR and TAM, leading to strand asymmetry of mutations due to transcription. Moreover, we recently discovered a novel function in TCR for Mediator, a conserved coactivator of transcription, and suggest its implication in mutagenesis. The aim of this interdisciplinary project is to improve our understanding of the mechanisms shaping mutational processes by deciphering how transcription and DNA repair influence mutagenesis, using an innovative approach based on microfluidics, genomics and computational analysis for mutation accumulation in budding yeast combined with mutagen exposure, as well as direct measuring of transcriptional activity. To shed light on the underlying mechanisms, we will: (i) decipher the impact of transcription and DNA repair on mutagenesis combined with mutagen treatment, using our microfluidic approach; (ii) develop a quantitative and predictive computational framework to decipher the signature of processes that induce mutations, combined with direct measurements of transcriptional activity; (iii) validate our quantitative model by performing mutation accumulation experiments and analyses based on its predictions. This project will fill important gaps in our understanding the mechanisms of mutational processes related to transcription at the origin of human diseases.