Widespread epistasis shapes RNA Polymerase active sites function and evolution

Multi-subunit RNA Polymerases are responsible for transcription in all kingdoms of life. At the heart of these msRNAPs is an ultra-conserved active site domain, the trigger loop, coordinating transcription speed and fidelity by critical conformational changes impacting multiple steps in substrate selection, catalysis and translocation. Previous studies have observed several different types of genetic interactions between eukaryotic RNA polymerase II TL residues, suggesting that the TL function is shaped by functional interactions of residues within and around the TL. The extent of these interaction networks and how they control msRNAP function and evolution remain to be determined. We aim to comprehensively dissect the TL interaction landscapes by deep mutational scanning in three eukaryotic msRNAPs of Saccharomyces cerevisiae. Our studies provide a powerful system to understand the plasticity of RNA polymerase mechanism and evolution.