The active sites of multisubunit RNA polymerases have a "trigger loop" (TL) that multitasks in substrate selection, catalysis, and translocation.To dissect the Saccharomyces cerevisiae RNA polymerase II TL at individual-residue resolution, we quantitatively phenotyped nearly all TL single variants en masse.Three mutant classes, revealed by phenotypes linked to Beauty Service/Accessories transcription defects or various stresses, have distinct distributions among TL residues.We find that mutations disrupting an intra-TL hydrophobic pocket, proposed to provide a mechanism for substrate-triggered TL folding through destabilization of a catalytically inactive TL state, BOSCH Serie 6 PCS7A5B90 Gas Hob - Stainless Steel LPG Convertible confer phenotypes consistent with pocket disruption and increased catalysis.Furthermore, allele-specific genetic interactions among TL and TL-proximal domain residues support the contribution of the funnel and bridge helices (BH) to TL dynamics.
Our structural genetics approach incorporates structural and phenotypic data for high-resolution dissection of transcription mechanisms and their evolution, and is readily applicable to other essential yeast proteins.