BIOLOGICAL CONSEQUENCES OF TARGETING BETA-1,4-GALACTOSYLTRANSFERASE TO 2 DIFFERENT SUBCELLULAR COMPARTMENTS

beta 1,4-galactosyltransferase is unusual among the glycosyltransferas es in that it is found in two subcellular compartments where it perfor ms two distinct functions. In the trans-Golgi complex, galactosyltrans ferase participates in oligosaccharide biosynthesis, as do the other g lycosyltransferases. On the cell surface, however, galactosyltransfera se associates with the cytoskeleton and functions as a receptor for ex tracellular oligosaccharide ligands. Although we now know much regardi ng galactosyltransferase function in these two compartments, little is known about how it is targeted to these different sites. By cloning t he galactosyltransferase gene products, certain features of the protei n have been identified that may be critical for its expression on the cell surface or retention within the Golgi complex. This article discu sses recent studies which suggest that a cytoplasmic sequence unique t o one galactosyltransferase isoform is required for targeting a portio n of this protein to the plasma membrane, enabling it to function as a cell adhesion molecule. These findings allow one to manipulate surfac e galactosyltransferase expression, either positively or negatively, a nd perturb galactosyltransferase-dependent cellular interactions durin g fertilization and development.