TALIN is a high-molecular-weight cytoskeletal protein concentrated at regions of cell-substratum contact1 and, in lymphocytes, at cell-cell contacts2,3. Integrin receptors are involved in the attachment of adherent cells to extracellular matrices4,5 and of lymphocytes to other cells6. In these situations, talin codistributes with concentrations of integrins in the cell surface membrane3,7-9. Furthermore, in vitro binding studies suggest that integrins bind to talin, although with low affinity10. Talin also binds with high affinity to vinculin11, another cytoskeletal protein concentrated at points of cell adhesion12. Finally, talin is a substrate for the Ca2+-activated protease, calpain II13,14, which is also concentrated at points of cell-substratum contact14. To learn more about the structure of talin and its involvement in transmembrane connections between extracellular adhesions and the cytoskeleton, we have cloned and sequenced murine talin. We describe a model for the structure of talin based on this sequence and other data. Homologies between talin and other proteins define a novel family of submembranous cytoskeleton-associated proteins all apparently involved in connections to the plasma membrane.
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