The Saccharomyces cerevisiae homologue of human Wiskott-Aldrich syndrome protein Las17p interacts with the Arp2/3 complex

Yeast Las17 protein is homologous to the Wiskott-Aldrich Syndrome protein, which is implicated in severe immunodeficiency. Las17p/Bee1p has been shown to he important for actin patch assembly and actin polymerization. Here we show that Las17p interacts with the Arp2/3 complex. LAS17 is an allele-spe cific multicopy suppressor of ARP2 and ARP3 mutations; overexpression resto res both actin patch organization and endocytosis defects in ARP2 temperatu re-sensitive (ts) cells. Six of seven ARP2 ts mutants and at least one ARP3 ts mutant are synthetically lethal with las17 Delta ts confirming function al interaction with the Arp2/3 complex. Further characterization of las17 D elta cells showed that receptor-mediated internalization of alpha factor by the Ste2 receptor is severely defective. The polarity of normal bipolar bu d site selection is lost. Las17-gfp remains localized in cortical patches i n vivo independently of polymerized actin and is required for the polarized localization of Arp2/3 as well as actin. Coimmunoprecipitation of Arp2p wi th Las17p indicates that Las17p interacts directly with the complex. Two hy brid results also suggest that Las17p interacts with actin, verprolin, Rvs1 67p and several other proteins including Src homology 3 (SH3) domain protei ns, suggesting that Las17p cascades destined for the Arp2/3p complex and ma y integrate signals from different regulatory the actin cytoskeleton.