The Prp19 WD40 Domain Contains a Conserved Protein Interaction Region Essential for Its Function

► The Prp19 WD40 domain adopts a distorted seven bladed β propeller fold ► A conserved surface patch is required for interaction with Cwc2 and for in vivo function ► Prp19 forms a 4:2 complex with Cwc2 in vitro and in vivo