Phosphatidylinositol-4-phosphate-binding protein that links Golgi membranes to the cytoskeleton and may participate in the tensile force required for vesicle budding from the Golgi. Thereby, may play a role in Golgi membrane trafficking and could indirectly give its flattened shape to the Golgi apparatus. May also bind to the coatomer to regulate Golgi membrane trafficking. May play a role in anterograde transport from the Golgi to the plasma membrane and regulate secretion. Has also been involved in the control of the localization of Golgi enzymes through interaction with their cytoplasmic part. May play an indirect role in cell migration. Has also been involved in the modulation of mTOR signaling. May also be involved in the regulation of mitochondrial lipids biosynthesis. Homodimer. Interacts with the coatomer complex. Interacts with MYO18A; the interaction is direct and may link Golgi membranes to the actin cytoskeleton. Interacts with GCNT1; may control its retention in the Golgi. Interacts with VPS35. Phosphatidylinositol 4-phosphate-binding and oligomerization participate in the recruitment onto Golgi membranes. Detected in muscle fibers of patients with mitochondrial diseases; not detected in normal muscle fibers. Activated by depletion of mitochondrial DNA. Phosphorylated. Modulates sensitivity to rapamycin. Tumors expressing this protein are more sensitive to rapamycin in vivo. Belongs to the GOLPH3/VPS74 family.