Cover Caption

About the cover: Ligand-induced receptor homodimerization triggering the initial step of cell signaling pathways. The juxtaposition of the cytoplasmic regions of the receptors makes it possible for kinase domains (▪) to phosphorylate (open square containing P) each other at the tyrosine residues (open oval containing Tyr). The positions of the phosphorylated tyrosines, which serve as docking sites for adaptor molecules, are schematically represented. See the article of Favoni and De Cupis on page 179 of this issue.