Fig. 7. Xin repeats inhibit binding of tropomyosin to actin filaments. Actin was mixed under polymerization conditions with a stable amount of tropomyosin and the indicated quantities of XR1-11. Actin filaments and associated proteins were precipitated under low-speed sedimentation conditions. In the absence of XR1-11 (X), only trace amounts of actin (A) were found in the pellet (control lane). The addition of only 0.5 µM XR1-11 resulted in precipitation of actin filaments together with the associated tropomyosin (T); larger quantities of recombinant Xin cause a dose-dependent increase of F-actin and a dose-dependent reduction of tropomyosin in the pellet.