Eukaryotic RNA Polymerase ⍺‐like Subunits Heterodimerize by Distinct Interaction Mechanisms

Abstract

DNA‐dependent RNA Polymerases (Pols) are present in every living cell and even encoded by some viruses. Pols are responsible for the process of transcription, and Pols from the three domains of life are constructed of a conserved core complex that includes a dimer of α or α‐like subunits that serve as a scaffold for Pol assembly. Bacteria and archaea each encode a single Pol that transcribes all forms of RNA, while eukaryotes encode three specialized Pols (I‐III) containing one of two distinct α‐like heterodimers. One α‐like heterodimer is shared between Pols I and III, while there is a paralogous Pol II heterodimer. The α‐like subunits are clinically relevant as mutations in the Pol I/III heterodimer are associated with Treacher Collins Syndrome and 4H Leukodystrophy, while mutations in the Pol II heterodimer are associated with Primary Ovarian Insufficiency. These mutations often result in defects in Pol assembly and/or activity, although the vast majority remain uncharacterized. It is currently unclear if heterodimer formation is functionally similar in α‐like subunit orthologs and/or paralogs and how these similarities and differences can be used to study the α‐like subunit associated diseases. To examine this, we mutated several regions of the yeast and human small α‐like subunits to test their contribution to heterodimer interaction using several types of biochemical and genetic assays. Here we show that different regions serve differential roles in heterodimerization, in a polymerase‐ and species‐specific manner, with both human subunits being more sensitive to mutations. This suggests that although the subunits are evolutionary conserved, they interact differently. More broadly, these findings help explain why some disease mutations have little to no effect in yeast and possibly other model systems, and may inform us how to make better disease models in the future.