RalA interaction with Exo84 and potential implications for exocyst activation. (A) The cryo-EM structure of yeast exocyst (PDB accession no. 5YFP) is shown colored by subunit, with an inset showing a superimposition of the X-ray structure of human RalA-Exo84 (PDB accession no. 1ZC3). (B) Model for RalA-mediated exocyst activation. RalA binding disrupts inter-subunit contacts that allosterically modulate the conformation of exocyst.