Clathrin mediated endocytosis (CME) in S. cerevisiae requires the dynamic interplay between many proteins at the plasma membrane. Actin polymerisation provides force to drive membrane invagination and vesicle scission. The WASp homologue in yeast, Las17 plays a major role in stimulating actin filament assembly during endocytosis. The actin nucleation ability of WASP family members is attributed to their WCA domain [WH2 (WASP homology2) domain, C central, and A (acidic) domains] which provides binding sites for both actin monomers and the Arp2/3 complex. In addition, the central poly-proline repeat region of Las17 is able to bind and nucleate actin filaments independently of the Arp2/3 complex. While Las17 is a key regulator of endocytic progression and has been found to be phosphorylated in global studies, the mechanism behind regulation of Las17 actin-based function is unclear. Therefore, the aims of this study were to investigate the post-translation modification of Las17 by phosphorylation, and to determine how this modification impacts on Las17 function both in vivo and in vitro.