Tail-interacting protein (TIP47) is a cytosolic protein essential for the transport of mannose-6-phosphate receptors (MPRs) from endosomes to the trans-Golgi compartments in cells. TIP47 is recruited from the cytoplasm to the late endosomal surface by the Ras-associated protein Rab9 GTPase, enabling it to bind more efficiently to MPR cytoplasmic domains. Recently, it was shown that TIP47 regulates the expression of Rab9, as expression of siRNA to TIP47 in transfected cells dramatically decreased the half-life of the Rab9 protein in addition to stabilizing the subcellular localization of Rab9. At least two isoforms of TIP47 are known to exist.