Signal transduction. FasL binds preassembled Fas.

The binding of a ligand to its receptor has always been viewed as the trigger for signal transduction to ensue. However, as Golstein explains in his Perspective, new findings (Chan et al. and Siegel et al.) suggest that the Fas receptor preassembles into trimers without the help of its ligand, and that this preassembly conditions ligand binding, and thus subsequent signal transduction of a death signal.