Microtubules in a Rac1(Q61L)-expressing PtK1 cell injected with Pak inhibitory fragment PBD/ID(H83L). Microtubules do not exhibit retrograde flow and undergo very little net growth. Epifluorescence image series were acquired on an inverted microscope (model TE300; Nikon) equipped with electronically controlled shutters, filter wheels, and a 14-bit cooled CCD camera (Orca II; Hamamatsu Corporation) controlled by MetaMorph® software (Universal Imaging Corp.) at 5-s intervals using a 60/1.4 NA Plan Apo objective lens (Nikon). Images were taken every 5 s and are played back at 15 frames/s. For still images, see Fig. 4, B and D of associated paper (J Cell Biol, 161:845-851, 2003).