Fig. 4. Tropomyosin is absent from regions of the leading edge containing the Arp2/3 complex. Cells were either unstimulated (A-D), or stimulated with EGF for 50 seconds (E-H) or 3 minutes (I-P), and double-labeled for the Arp2/3 complex (anti-p34; A,E,I,M) and tropomyosin (LC24, B,F,J; IV15, N). Double-labeling overlays are shown in C, G, K and O (red, tropomyosin; green, the Arp2/3 complex). Phase contrast images are present in D, H, L and P. Bar, 10 µm. Arrows indicate regions at the leading edge where the Arp2/3 complex is localized demonstrating the absence of tropomyosin.