The protein encoded by this gene is a receptor for mannose-6-phosphate groups on lysosomal enzymes. The receptor forms a homodimer or homotetramer for intracellular targeting of lysosomal enzymes and export of newly synthesized lysosomal enzymes into the cell secretions. The receptor is an integral membrane protein which localizes to the trans-Golgi reticulum, endosomes, and the plasma membrane.