Mouse spleen lymphocytes synthesize a protein which comigrates with skeletal muscle alpha-actinin on two-dimensional gel electrophoresis and is immunoprecipitated by an antibody directed against skeletal muscle alpha-actinin. Mouse lymphocyte alpha-actinin is present in membrane fractions, and is immunoprecipitated from lymphocyte detergent lysates by an antiserum made against these purified membranes. The anti-alpha-actinin activity of this antiserum is not adsorbed after incubation with fixed intact lymphocytes. Lymphocyte alpha-actinin does not bind concanavalin A and it is inaccessible to lactoperoxidase-catalyzed surface iodination. Double immunofluorescence shows that alpha-actinin moves concurrently along the cell membrane with redistributed surface immunoglobulins and Thy-1 antigen, and remains associated up to 30 min with surface aggregates of these receptors. Our results suggest that lymphocyte alpha-actinin, as defined by molecular weight and cross reactivity with the antibody against the muscle protein, (a) is associated with the cell membrane, (b) is not expressed at the cell surface, and (c) participates in the movement of surface receptors.

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