Autophagy is a process of intracellular bulk degradation in which cytoplasmic components including organelles are sequestered within double-membrane vesicles that deliver the contents to the lysosome/vacuole for degradation. Beclin 1, the mammalian homologue of yeast Atg6, was first identified Bcl-2-interacting protein. Beclin 1 localizes to the trans-Golgi network, and forms a complex with phosphatidylinositol 3-kinase. Beclin 1 is essential for early autophagosome formation.