Adaptive variation in mutagenesis driven by protein self-assembly

Mutations supply raw material for evolution. However, most are not adaptive. Thus, shifts in mutagenesis are typically transient. Nonetheless, modelling predicts that a heritable but revertible 'mutagenesis switch' would win in many selective landscapes. Here we report that prions formed by DNA repair proteins endow Saccharomyces cerevisiae with this capacity, sparking heritable variation in mutagenesis rates in evolving populations from the laboratory, nature, and the clinic. Self-templating transforms the functions and interactions of these DNA fidelity factors, enabling resilience to genotoxic stress and the emergence of drug resistance. In the fungal pathogen C. albicans, which diverged from S. cerevisiae ~300 million years ago, factors supporting prion inheritance promote the evolution of resistance to fluconazole, a mainline antifungal. Our findings suggest that protein self-assembly, a collective molecular behavior that is common among DNA replication and repair factors, can materialize epigenetic memory that tunes the balance of genome diversification and fidelity to expand adaptive opportunities. Overall design: To understand the effects of yeast prions on gene expression, we measured mRNA levels in a variety [PRION+] strains alongside naive and cured controls.