Abstract
The polymerization of actin is catalysed by the Arp (actin-related protein) 2/3 complex, which acts downstream of a variety of receptors and signalling cascades. Intermediary molecules such as cortactin bind to the Arp2/3 complex and stimulate its activity, thus promoting actin polymerization and actin filament stabilization. New data in this issue of the Biochemical Journal by the Kapus group suggest that cortactin is reciprocally regulated by filamentous (F) actin and tyrosine kinases. This suggests a new paradigm for considering the cellular processes that regulate the dynamic organization of the actin cytoskeleton.