New bend on budding

JCB • VOLUME 170 • NUMBER 7 • 2005 1016 New bend on budding OPII vesicles form from the endoplasmic reticulum (ER). Now, Marcus Lee, Randy Schekman (University of California, Berkeley), and Lelio Orci (University of Geneva, Switzerland) find that insertion of the amphipathic helix of the Sar1 GTPase causes membrane deformation that initiates, and eventually ends, this vesicle formation process. The group investigated how COPII coats shape the ER by examining in isolation how each set of COPII proteins—Sar1, Sec23/24, and Sec13/31—influences membrane curvature. When activated Sar1-GTP was incubated with spherical liposomes, the researchers saw that the spheres strikingly developed long, narrow tubules 26 nm in diameter. They then determined that insertion of Sar1’s helix into the lipid bilayer is responsible for this transformation. “When you stick an object C