UCSF

Polymerization of actin into filaments powers diverse cellular functions, and a key way that cells build distinct types of actin networks is by using different actin nucleation factors. We identified a new vertebrate actin nucleation factor, junction-mediating and regulatory protein (JMY, pronounced "jammy"). JMY combines de novo nucleation by a Spire-like mechanism with activation of the Arp2/3 complex to rapidly generate branched actin networks. JMY localizes to the leading edge of motile cells, and contributes to cell motility. Since the Arp2/3 complex requires pre-existing filaments for its branching nucleation activity, we hypothesize that JMY contributes to cell motility by nucleating filaments, which then serve as substrates for JMY-activated Arp2/3 nucleation.