This is a 10 x solution that contains 500 mM KCl, 20 mM MgCl2?and 10 mM ATP in 100 mM Tris, pH 7.5. It is used to add to G-actin solutions in A-buffer (General actin buffer (Cat. #?BSA01), 0.2 mM ATP (Cat. #?BSA04) and 0.5 mM DTT) to induce polymerization into F-actin.