Beclin is a Bcl-2 binding protein. Its structure includes a Bcl-2 binding coiled-coil region, and a leucine-rich nuclear export signal (NES). Beclin protein colocalizes with intracytoplasmic organelles and nuclei in normal COS7 and MCF7 cells. Beclin interaction with Bcl-2 may be involved with host viral defense, since over expression of beclin inhibits Sindbis virus replication and expression of beclin lacking the Bcl-2 binding domain has no antiviral effects.