A MULTIVALENT PDZ-DOMAIN PROTEIN ASSEMBLES SIGNALING COMPLEXES IN A G-PROTEIN-COUPLED CASCADE

How are signalling molecules organized into different pathways within the same cell? In Drosophila, the inaD gene encodes a protein consisti ng of five PDZ domains which serves as a scaffold to assemble differen t components of the phototransduction cascade, including the principal fight-activated ion channels, the effector phospholipase C-beta and p rotein kinase C, Null inaD mutants have a dramatically reorganized sub cellular distribution of signalling molecules, and a total loss of tra nsduction complexes. Also, mutants defective in a single PDZ domain pr oduce signalling complexes that lack the target protein and display co rresponding defects in their physiology. A picture emerges of a highly organized unit of signalling, a 'transducisome', with PDZ domains fun ctioning as key elements in the organization of transduction complexes in vivo.