Binding of MRP8 or MRP14 to tubulin. (A) Prepolymerized and Taxol-stabilized MTs were incubated with MRP8/MRP14 or MRP8/phospho-MRP14 complexes at an equimolar ratio (tubulin dimer to MRP8/MRP14 = 1:1) in the absence or presence of 60 μM calcium. Binding to tubulin filaments was then analyzed by spin-down binding assays and Coomassie blue stainings after SDS-PAGE. (B) Binding to tubulin was analyzed as described in panel A using isolated subunits of MRP8, MRP14, or phospho-MRP14. The interaction of MRP8/MRP14 complexes with tubulin was not affected by addition of up to 300 mM NaCl (data not shown). All experiments presented in this figure were performed at least 3 times.