Cristae, the complex involutions of the mitochondrial inner membrane, vastly increase the surface area across which ATP synthase can generate a proton gradient. Now, new findings from Jean Velours (Universite Victor Segalen, Bordeaux, France) and colleagues suggest that ATP synthase may be important in forming cristae in the first place. Figure Mitochondrial cristae (top) turn onion shaped in the absence of an ATP synthase subunit (bottom). Velours' theory is that oligomerization of ATP synthase in the mitochondrial inner membrane helps tubulate the membrane. This idea was first suggested based on the zippered rows of ATP synthase molecules visible on the cristae of Paramecium mitochondria. Velours does not yet know if yeast has the same arrangement. But in the new work he detects the formation of yeast ATP synthase oligomers biochemically. Loss of the nonessential e or g subunits of ATP synthase both disrupts oligomerization and results in mitochondria that lack conventional cristae. The mutant mitochondria have an inner membrane that is wound around itself in an onion shape.The new evidence provides only a correlation between oligomerization and cristae formation, but Velours is now planning more direct electron microscopy experiments to see if oligomerization is indeed responsible for curving the membrane into cristae. ▪ Reference: Paumard, P., et al. 2002. EMBO J. 21:221–230. [PubMed]