Fig. 4. Examples of higher-order organization of PDZ domains found in signaling proteins. Proteins are indicated in black lines scaled to the length of the primary sequence of the protein; PDZ domains are shown in yellow. Other domains are indicated as abbreviations (from SMART) (Schultz et al., 2000) as follows: SH3, Src-homology 3 domain; GuK, guanylate-kinase-like domain; LIM, zinc-binding domain present in Lin-11, Isl-1, Mec-3; PH, pleckstrin-homology domain; RBD, Raf-like Ras-binding domain; RhoGEF, Rho-like GTP-exchange factor; DAX, Dishevelled- and axin-homology domain; DEP, Dishevelled-, Egl-10- and pleckstrin-homology domain.