Figure 4.

Effect of utrophin on F-actin depolymerization. (A) Time course of actin depolymerization in the absence (●) or presence of utrophin (○). F-actin was preincubated alone or in a 10:1 M ratio with utrophin and filament depolymerization was induced by dilution to final actin and NaCl concentrations of 2 μM and 4.5 mM, respectively. At various times postdilution, samples were centrifuged at 100,000 × g for 20 min and the fraction of F-actin remaining was determined densitometrically from Coomassie blue-stained gels loaded with equal volumes of supernatants and pellets. Time points include centrifugation time. (B) F-actin was preincubated with increasing amounts of utrophin to give the indicated utrophin/actin monomer ratio and depolymerization was initiated by dilution as described above. Thirty minutes after initiation of depolymerization, samples were centrifuged at 100,000 × g and the percentage of F-actin remaining was determined as in A. The data represent the average (± SEM) from five (A) and three (B) independent experiments.