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Figure 6


Fig. 6. Stimulation of branched actin filament assembly by IQGAP1. (A) Effects of IQGAP1 on actin (5% labeled with pyrene) assembly in the presence of N-WASP and the Arp2/3 complex were monitored using a pyrene-actin fluorescence assay. Note that maximal stimulation of assembly was achieved at 30 nM IQGAP1, and that higher and lower concentrations stimulated less or not at all. (B) Actin assembly stimulation by IQGAP1 requires N-WASP plus Arp2/3 complex. (C) IQGAP1-stimulated assembly of branched actin filament networks observed directly by TIRF microscopy. (D) Total lengths of actin filaments observed by TIRF microscopy were measured as a function of time, for samples containing or lacking IQGAP1 or activated Cdc42, a previously described for the N-WASP activator (Rohatgi et al., 1999). Maximum rates of actin assembly were achieved in the IQGAP1 sample. (E) The same micrographs were used to determine the number of filament branch points per µm of actin filament as a function of time. Note that the IQGAP1 and Cdc42 samples quickly attained a filament branch density four- to fivefold greater than the control sample that contained neither IQGAP1 nor Cdc42.





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