The ability to regulate the function of specific proteins using cell-permeable molecules can
be a powerful method for interrogating biological systems. To bring this type of" chemical
genetic" control to a wide range of proteins, we recently developed an experimental system
in which the stability of a small protein domain expressed in mammalian cells depends on
the presence of a high affinity ligand. This ligand-dependent stability is conferred to any
fused partner protein. The FK506-and rapamycin-binding protein (FKBP12) has been the …