Fig. 4. Catastrophes can occur in the zyxin-free zone of focal adhesions. (A) A frame from a video sequence of a cell co-transfected with mCherry-paxillin (red) and GFP-zyxin (green). Bar 10 µm. (B,C) Enlargement of areas at the leading edge (B) and trailing edge (C) of the cell (paxillin, red; zyxin, green). The intensity profiles of paxillin (red lines) and zyxin (green lines) along a line (white) of width one pixel are shown. Paxillin extends more distantly towards the cell edge. The image is a representative example from 15 cells. (D) A frame from a video sequence of a cell co-transfected with GFP-EMTB (blue) to visualize microtubules, Cerulean-zyxin (green) to mark late adhesions and mCherry-paxillin (red) to mark both early and late adhesions. Bar, 10 µm. The boxed area is enlarged to the right (E,F). (E) Enlarged frame sequence of microtubules (green) and paxillin (pink). (F) Enlarged frame sequence of microtubules (green) and zyxin (red). A catastrophe occurred at the 20-second time-point at the distal zyxin-free end of a focal adhesion. Time, seconds. Arrows show the direction of microtubule movement. (G) Enlarged frame sequence of the focal adhesion from E and F, showing zyxin (green) and paxillin (red). The arrows point at the zyxin-free distal end of the focal adhesion.