A membrane cytoskeleton from Dictyostelium discoideum. III. Plasma membrane fragments bind predominantly to the sides of actin filaments.

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Abstract
The binding between sonicated D. discoideum plasma membrane fragments and F-actin on Sephacryl S-1000 beads was competitively inhibited by myosin subfragment-1. This inhibition is MgATP-sensitive, exhibits a Ki of .apprx. 5 .times. 10-8 M, and is reciprocal, since membranes inhibit the binding of 125I-heavy meromyosin to F-actin on beads. Membrane binding and S-1 binding to F-actin on beads are mutually exclusive and, therefore, the membrane fragments bind predominantly to the sides, rather than to the ends, of the actin filaments. This conclusion is supported by electron micrographs that show many lateral associations between membrane fragments and bead-associated actin filaments. Such lateral associations could play an important role in the organization and lateral movement of membrane proteins by the cytomusculature.