The seven-subunit, Arp2/3 complex localizes to the leading protrusions of migrating cells, where it nucleates actin assembly. On , Gang Liu and colleagues hypothesize that an efficient way to target such a large, stable complex to a specific region of the cell might be to localize the mRNAs for its component subunits to the same region. By using sensitive FISH techniques, the authors show that, as predicted, all the mRNAs for the Arp2/3 complex are targeted to the leading protrusions of chick embryo and human foreskin fibroblasts. This localization depends on serum factors, which suggests that it represents a cellular response to extracellular stimuli, and on actin filaments, microtubules and the presence of myosin motors. How the Arp2/3-complex mRNAs are localized to the leading protrusions of fibroblasts and then anchored is not yet known, but these results provide the first evidence for localization of all the mRNAs of a multisubunit protein complex to its site of assembly and function.
