EXPERIMENTAL FIGURE 4-15 Double-label fluorescence microscopy can visualize the relative distributions of two proteins. In double-label fluorescence microscopy, each protein must be labeled with a different fluorochrome. (a) A cultured cell was fixed and permeabilized and then incubated with Rhodamine-labeled phalloidin, a reagent that specifically binds to filamentous actin. It was also incubated with rabbit antibodies to tubulin, the major component of microtubules, followed by a fluorescein-labeled secondary goat–anti-rabbit antibody. (b) The upper panels show the fluorescein-stained tubulin (left) and Rhodamine-stained actin (right), and the lower panel shows the electronically merged images.

[Part (b) courtesy of A. Bretscher.]