Actin-related protein 3 <p>Actin-related proteins are defined broadly as proteins that have significant (30-60%) amino acid identity to conventional actin. Ten members, named Arp1-Arp10, have been identified in budding yeast [<cite idref="PUB00035125"/>] and play diverse roles in the cell, ranging from the regulation of actin to chromatin remodeling. Actin and Arps are part of a large, ancient family of ATPases that include heat shock proteins and sugar kinases.</p> <p>Actin-related protein 3 (Arp3) shares about 35-40% amino acid identity with conventional actin [<cite idref="PUB00035126"/>]. Arp3 is only found in the cell as a member of a 7-subunit complex, known as the Arp2/3 complex. The Arp2/3 complex is composed of Arp3, Arp2 and five novel proteins: p40 (ARPC1), p35 (ARPC2), p19 (ARPC3), p18 (ARPC4), and p14 (ARPC5). The Arp2/3 complex has been found in all eukaryotes and is highly conserved across species.</p> <p>Arp2/3 binds to pre-existing actin filaments and nucleates new daughter filaments, and thus becomes incorporated into the dynamic actin network at the leading edge of motile cells and other actin-based protrusive structures [<cite idref="PUB00035127"/>]. In order to nucleate filaments, Arp2/3 must bind to a member of the N-WASp/SCAR family protein [<cite idref="PUB00020552"/>]. rp2 and Arp3 are thought to be brought together after activation, forming an actin-like nucleus for actin monomers to bind and create a new actin filament. In the absence of an activating protein, Arp2/3 shows very little nucleation activity.</p> <p>Recent research has focused on the binding and hydrolysis of ATP by Arp2 and Arp3 [<cite idref="PUB00035128"/>], and crystal structures of the Arp2/3 complex have been solved [<cite idref="PUB00022758"/>].</p>