REGULATION OF YEAST GOLGI GLYCOSYLATION - GUANOSINE DIPHOSPHATASE FUNCTIONS AS A HOMODIMER IN THE MEMBRANE

The Golgi Iumenal GDPase plays an important role in the mannosylation of proteins and Lipids of Saccharomyces cerevisiae by regulating the a mount of GDP-mannose available in the Golgi lumen. The enzyme makes av ailable GRIP as an antiporter to be coupled with entry of GDP-mannose into the Golgi lumen from the cytosol. Using radiation inactivation an d target analysis, we have now determined the functional molecular mas s of the GDPase within the GoIgi membrane and whether or not the enzym e has functional associations with other Golgi membrane proteins, incl uding mannosyltransferases and the GDP-mannose transporter. The functi onal size of the GDPase was found to be approximately twice the estima ted structural target size of the protein; this strongly suggests that the GDPase protein in situ functions as homodimer and does not requir e association with other membrane proteins for its function.