A new side of xylosides and their close relatives: Co-localization mapping of glycosyl transferases in the functional Golgi

beta-Xylosides and other glycosides prime the synthesis of protein-free glycan chains when fed to cells. To co-localize enzymes that initiate and extend these chains, we incubated these freely permeable accepters with intact functional Golgi that transport exogenously supplied UDP-[H-3]Gal. Golgi compartments having the appropriate transferases and sugar nude otide transporters glycosylate the added accepters, and since these Golgi do not carry out intervesicular transport, any additional glycosylations of the added acceptor must occur in same sealed compartment. This gives evidence for co-localization of additional transferases in the same compartment. In addition, some of the transferases synthesizing other glycoconjugates are located in the same Golgi subcompartments and must compete for transported sugar donors. Labeling of added accepters consumes the limited amount of donors and leaves less available for glycosylating endogenous accepters in the same compartment. Careful structural analysis of the glycans made in the presence and absence of added accepters shows which transferases are co-localized. This review highlights successes and problems encountered using these two approaches. Together they offer an opportunity to do high resolution mapping of the functional Golgi within the cis, medial and trans continental borders.