Binding of tau to actin detected by solid phase assay. Wells were coated with 50 μl G-actin and F-actin (5 μg/ml) from skeletal muscle and platelets, respectively. Aliquots of different concentrations of tau (from 0.03 to 0.55 μM) were incubated with actin in binding buffer (50 mM Hepes containing 0.5 mM EGTA and 0.5 mM MgCl2, pH 7.5). Immunoreactivity was monitored in the solid phase assay using secondary antibody-labelled HRP. Each point represents the mean of five determinations.