Ligand- and Antibody-Affinity Purification of the Epidermal Growth Factor Receptor

The study of the mechanism by which growth factors transmit a mito-genic signal through the plasma membrane has been greatly facilitated by the use of the EGF receptor as a model system. Binding of EGF to its receptor initiates a cascade of cellular events, presumably through stimulation of its intrinsic tyrosine-specific protein kinase activity, which culminate in DNA synthesis and cell division (reviewed by Carpenter, 1987). Studies using purified EGF receptor have helped to determine the mechanism of its activation and elucidate its primary structure (Downward et al., 1984a). The EGF receptor has a molecular weight of 170 kDa. A single, membrane-spanning stretch of 23 amino acids links the extracellular, EGF binding domain to the cytoplasmic kinase domain (Ullrich et al., 1984). A C-terminal 15 kDa domain carries the major autophosphorylation sites of the receptor and is connected to the cytoplasmic domain through a putatively flexible, protease-sensitive link (Downward et al., 1984a).