ATP-binding component of the Arp2/3 complex, a multiprotein complex that mediates actin polymerization upon stimulation by nucleation-promoting factor (NPF). The Arp2/3 complex mediates the formation of branched actin networks in the cytoplasm, providing the force for cell motility (By similarity). Seems to contact the pointed end of the daughter actin filament (By similarity). In addition to its role in the cytoplasmic cytoskeleton, the Arp2/3 complex also promotes actin polymerization in the nucleus, thereby regulating gene transcription and repair of damaged DNA (By similarity). The Arp2/3 complex promotes homologous recombination (HR) repair in response to DNA damage by promoting nuclear actin polymerization, leading to drive motility of double-strand breaks (DSBs) (By similarity). Component of the Arp2/3 complex composed of actr2/arp2, actr3/arp3, arpc1 (arpc1a or arpc1b), arpc2, arpc3, arpc4 and arpc5. Belongs to the actin family. ARP3 subfamily.