ActA and human zyxin harbour Arp2/3-independent actin-polymerization activity

The actin cytoskeleton is a dynamic network that is composed of a variety o f F-actin structures. To understand how these structures are produced, we t ested the capacity of proteins to direct actin polymerization in a bead ass ay in vitro and in a mitochondrial-targeting assay in cells. We found that human zyxin and the related protein ActA of Listeria monocytogenes can gene rate new actin structures in a vasodilator-stimulated phosphoprotein-depend ent (VASP) manner, but independently of the Arp2/3 complex. These results a re consistent with the concept that there are multiple actin-polymerization machines in cells. With these simple tests it is possible to probe the spe cific function of proteins or identify novel molecules that act upon cellul ar actin polymerization.