RUN and FYVE domain-containing protein 1 (RUFY1, aka RABIP4, ZFYVE12) associates with phosphatidylinositol 3-phosphate in membranes of early endosomes and may participate in early endosomal membrane trafficking. RUFY1 is localised to the cytoplasm and early endosomal membrane, the latter being the predominant localisation after RUFY1 is phosphorylated. Cytoplasmic tyrosine-protein kinase BMX (BMX, aka ETK) is a a downstream tyrosine kinase of PI3-kinase which, through its SH2 and SH3 domains, binds to and phosphorylates RUFY1 at Tyr-389 and Tyr-400. These phosphorylations are essential for endosomal localisation (Yang et al. 2002).