Class IA phosphoinositide-3 kinases (PI3Ks) are heterodimeric enzymes that regulate many signal transduction pathways. The p85 regulatory subunit recruits the p110 catalytic subunit to the membrane, where p110 phosphorylates inositol lipids. Recent studies present evidence for an additional role for p85alpha in the regulation of actin cytoskeleton. Okkenhaug and Vanhaesebroeck discuss these results and ask whether experiments describing p85alpha knockout mice need to be reinterpreted.