Desmin is the intermediate filament (IF) protein that polymerizes to form the desniin IF of skeletal muscle. It is found in smooth, skeletal, and cardiac muscle. The desmin IF links desmosomes of cardiac muscle, thus serving to stabilize cell junctions. Actin is the protein of microfilaments-the smallest diameter filament of the cytoskeleton. Actinin is an actin-associated protein (an actin-bundling protein) that serves to cross4ink actin bundles and anchor actin filaments to the cell membrane. Clathrin forms a basket or cage around endocytotic vesicles. Vimentin is a widely distributed IF protein present in many cells of mesodermal origin.