GLYCOPROTEIN RECYCLING TO THE GALACTOSYLTRANSFERASE COMPARTMENT OF THE GOLGI-COMPLEX

The recycling of plasma membrane glycoproteins to the Golgi complex is well established, but it is not clear which Golgi subcompartments rec eive this traffic. To date, recycling into the trans-Golgi compartment that contains sialyltransferase and the early Golgi region that conta ins alpha-mannosidase I has been demonstrated. However, transport into other Golgi compartments has not been reported. In this study we test ed the return of cell surface glycoproteins to the Golgi galactosyltra nsferase compartment using the ldlD mutant of Chinese hamster ovary ce lls. The cation-independent mannose 6-phosphate/insulin-like growth fa ctor-II receptor recycled through this Golgi region with a half-time o f 4 h and was transported to the sialyltransferase compartment as well . Because galactosyltransferase and sialyltransferases are probably lo cated in different trans-Golgi regions in Chinese hamster ovary cells, these results suggest that the two compartments each receive recyclin g traffic or that recycling glycoproteins enter one region and are the n transported to the other. The extent of cell surface protein recycli ng through the galactosyltransferase compartment was also studied. At least 10 different glycoproteins were transported from the cell surfac e to this Golgi region. Moreover, our results suggest that recycling g lycoproteins make up 12-25% of the flux of cell surface glycoproteins through the Golgi galactosyltransferase compartment; the balance is co mprised of newly made glycoproteins.