The WASp homologue Las17p functions with the WIP homologue End5p/verprolin and is essential for endocytosis in yeast

Several end mutations that block the internalisation step of endocytosis in Saccharomyces cerevisiae also affect the cortical actin cytoskeleton [1], END5 encodes a proline-rich protein (End5p or verprolin) required for a polarised cortical actin cytoskeleton and endocytosis [2,3], End5p interacts with actin [4], but its exact function is not yet known. To help elucidate End5p function, we sought other End5p-interacting proteins and identified the LAS17/BEE1 gene (encoding the yeast homologue of the human Wiskott-Aldrich Syndrome protein, WASp) as a high-copy-number suppressor of the temperature-sensitive growth and endocytic defects of end5-1 cells (carrying a frameshift mutation affecting the last 213 residues of End5p), LAS17 is unable to suppress a full deletion of END5 (end5 Delta), however, suggesting that the defective End5-1p in end5-1 mutants may be stabilised by Las17p, The amino terminus of Las17p interacts with the carboxyl terminus of End5p in the yeast two-hybrid system and similar interactions have been shown between WASp and a mammalian End5p homologue, WASp-interacting protein (WIP) [5]. As las17 Delta deletion mutants are blocked in endocytosis, we conclude that Las17p and End5p interact and are essential for endocytosis.