The focal adhesions of tissue culture cells provide a convenient model for analysis of the molecular basis of cell adhesion. These sites have been recognized for decades as sites of tight structural attachment of the cell membrane to the underlying substrate. Although classical focal adhesions can be found only in cultured cells, focal adhesions appear to be morphologically and functionally analogous to sarcolemmal dense plaques of smooth muscle cells in vivo [23]. On the outside of the cell membrane, ECM components, such as fibronectin, vitronectin, laminins and collagens are found. The primary transmembrane components of focal adhesions are integrins, a large family of transmembrane heterodimers [51]. Members of this protein superfamily act as receptors for ECM components on the outside of the cell, and interact with the cytoskeletal components of the focal adhesions inside the cells [95]. For the past decade, the number of proteins identified at the focal adhesion cytoplasmic face has expanded greatly. Analysis of their physical interactions has lead to the proposal of several models to describe the molecular links that anchor actin to the plasma membrane at these sites. Currently, it is thought that multiple mechanisms may exist to connect the actin cytoskeleton to integrins. Talin is a major structural element of focal adhe-