Autophagy, the process of bulk degradation of cellular proteins throμgh an autophagosomic-lysosomal pathway is important for normal growth control and may be defective in tumor cells. It is involved in the preservation of cellular nutrients under starvation conditions as well as the normal turnover of cytosolic components and is negatively regulated by TOR (Target of rapamycin). PIST, a PDZ-containing protein, was discovered in a yeast two-hybrid system as a binding partner to Beclin-1, a Bcl-2-interacting protein homologous to the yeast autophagy gene apg6. Experiments with mutant PIST proteins lacking the PDZ domain showed that PIST interaction with Beclin-1 throμgh its coiled-coil domain can modulate Beclin-1 activity and sμggest that PIST interactions with other proteins throμgh its PDZ domain may regulate the activity of PIST and Beclin-1.