Figure 1.
Polymerization and depolymerization of V159N actin were measured by light scattering at 400 nm. (A) Polymerization of 5 μM wild-type or V159N actin was initiated by the addition of 0.1 M KCl, 2 mM MgCl2, and 0.5 mM ATP. (B) Depolymerization was measured by diluting 5 μM F-actin to 0.5 μM in the polymerization buffer. The half time of depolymerization for wild-type actin is 114 s (n = 4, SD = 18), and for V159N actin is 355 s (n = 5, SD = 155). (C) Cofilin-accelerated depolymerization was observed by diluting 5 μM F-actin to 0.5 μM in polymerization buffer containing 0.5 μM yeast cofilin. (D) The critical concentration was measured by pelleting filamentous actin from steady-state reactions containing different concentrations of actin. Supernatants and pellets were analyzed by SDS/PAGE, and actin was quantified by densitometry. The critical concentration of V159N was measured three times, and the values ranged from 0 to 20 nM. The critical concentration of wild-type yeast actin is 160 nM.