Fig. 1.

The autophagic process. In response to a variety of cellular stresses a class III PI3 kinase/Beclin 1 complex initiates formation of an isolated double membrane (the membrane nucleation process) and subsequent membrane elongation. The membrane then fuses on itself, forming the distinctive double-membrane autophagosome. Autophagosomes ultimately fuse with lysosomes, and their cargo is degraded, providing fuel and elemental building blocks to preserve vital cellular functions