The experimental system Previously, we have noted that incubation of egg extract without addition of chromatin promoted the formation of flat membrane cisternae studded with pore complexes, termed annulate lamellae (AL) (Dabauvalle et al., 1991). In a subsequent study, we found that AL formation apparently depleted a specific type of membrane vesicles from the egg extract that were required for NPC assembly from the egg extract (Ewald et al., 1997). Once these pore-forming Supplementary material available online at