x that functions in transport of cargoes and organelles on microtubules. In human cells, this complex also contains the distantly related ARP11 as well as globular actin and the ABP, CapZ (Eckley 1999 ; Eckley and Schroer, 2003 ). The ARP2 and ARP3 dimer is definitely portion of a seven-subunit complex that nucleates polymerization of de novo actin filaments and branched networks beneath the plasma membrane (examined in Pollard 2000 ). The 3D structure of the ARP2/3 complex.