The Arp2/3 complex: a multifunctional actin organizer

The actin-related proteins (Arps) constitute a recently characterized famil y of proteins, many of which function as members of multiprotein complexes. The discovery that two family members, Arp2 and Arp3, act as multifunction al organizers of actin filaments in all eukaryotes has generated much excit ement. Over the past two years, newly discovered properties of the Arp2/3 c omplex have suggested a central role in the control of actin polymerization . First, it promotes actin assembly on the surface of the motile intracellu lar pathogen Listeria monocytogenes. Second, it can nucleate and cross-link actin filaments in vitro. Third, it localizes with dynamic actin-rich spot s of mammalian cells suggesting a role in protrusion; it is found in cortic al actin patches in the budding and fission yeasts where it may control pat ch movement and cortical actin function. Clearly, the complex has a central role in actin cytoskeletal function and will be the subject of much resear ch in the coming years.