Functions as actin-binding component of the Arp2/3 complex which is involved in regulation of actin polymerization and together with an activating nucleation-promoting factor (NPF) mediates the formation of branched actin networks. Seems to contact the mother actin filament (By similarity). Component of the Arp2/3 complex composed of arp2, act2, arc1/p41-ARC, arc2/p34-ARC, arc3/p21-ARC, arc4/p20-ARC and arc5/p16-ARC. Belongs to the ARPC2 family.