Inhibition of relaxation activity by ICRF-193. Relaxation reactions were performed with (A) wt topo IIβ in the presence of 0, 1, 2, 3, 4, 5 or 6 µM ICRF-193 as indicated or (B) βS165R in the presence of 0, 1, 2, 3, 4, 5, 6 or 7 µM ICRF-193 as indicated.