Beclin 1 is the first identified mammalian gene to mediate autophagy and also has tumor suppressor and antiviral function. Autophagy, a process of bulk protein degradation through an autophagosomic lysosomal pathway, is important for differentiation, survival during nutrient deprivation, and normal growth control, and is often defective in tumor cells. Beclin 1 was originally isolated in a yeast two hybrid screen to identify Bcl 2 binding partners and maps to a tumor susceptibility locus on human chromosome 17q21 that is frequently monoallelically deleted in human breast, ovarian and prostate cancer. Beclin 1 encodes an evolutionarily conserved 52kDa coiled coil protein that is expressed in human muscle, epithelial cells and neurons.