TABLE 1.

Summary of in vitro kinetic data for purified WT and mutant actins

All actin concentrations were 2.5 μm except for assays with N-WASP, which were performed with 1 μm actin.

Strain	Nucleation time (approx.)		Polymerization rate			TIRF microscopy
	−Arp2/3	+Arp2/3	−Arp2/3	+Arp2/3	+NWASP	Branch initiation
	s		a.u./s
WT	250	300	2.7	8.2	5.0	3.5 min
K118M	250	350	2.7	5.2	3.8	5 min
K118N	NAa	150	6.2	5.6	4.0	NAb

^a No nucleation lag was apparent from the light scattering data.

^b Kinetic analysis of K118N actin with TIRF was not possible due to labeling effects on the actin.