ROLES FOR MANNOSE-6-PHOSPHATE RECEPTORS IN LYSOSOMAL-ENZYME SORTING, IGF-II BINDING AND CLATHRIN-COAT ASSEMBLY

Two related transmembrane proteins in mammalian cells bind the mannose 6-phosphate recognition marker present on all soluble lysosomal hydro lases. Recent studies of cells that express only one or neither of the se proteins have shed light Mot only on their function in directing ly sosomal enzymes into the endocytic pathway but also on their critical role in transport vesicle formation in the trans Golgi network. One of these proteins also binds insulin-like growth factor II (IGF-II) and may be an important part of the IGF-dependent system that regulates de velopment.