Our research interfaces between chemistry and biology to understand fundamental cellular processes at the level of chemical and physical principles. We ask the following questions: how does a cell provide sophisticated temporal and spatial control for complex biological processes? What are the molecular principles that underlie biological recognition and regulation? Our attention currently focuses on a pair of GTPases in the signal recognition particle (SRP) and the SRP receptor (SR) that act as molecular switches to control the delivery of newly synthesized proteins to cellular membranes.