Eukaryotic RNA polymerase subunit RPB8 is a new relative of the OB family

RNA polymerase II subunit RPB8 is an essential subunit that is highly conserved throughout eukaryotic evolution and is present in all three types of nuclear RNA polymerases. We report the first high resolution structural insight into eukaryotic RNA polymerase architecture with the solution structure of RPB8 from Saccharomyces cerevisiae. It consists of an eight stranded, antiparallel β-barrel, four short helical regions and a large, unstructured omega-loop. The strands are connected in classic Greek-key fashion. The overall topology is unusual and contains a striking C₂ rotational symmetry. Furthermore, it is most likely a novel associate of the oligonucleotide/oligosaccharide (OB) binding protein class.