The 17-Residue Transmembrane Domain ofß-Galactoside a2,6-Sialyltransferase Is Sufficient for Golgi Retention

ß-Galactoside a2,6-sialyltransferase (ST) is a type II integral membrane protein of the Golgi apparatus involved in the sialylation of N-linked glycans . A series of experiments has shown that the 17-residue transmembrane domain of ST is sufficient to confer localization to the Golgi apparatus when transferred to the corresponding region of a cell surface type II inTHE Golgi apparatus is a highly organized organelle composed of networks of membrane-bound tubules, cisternae, and vesicles. Recent studies have shown that the Golgi apparatus is further differentiated into distinct subcompartments, each having a distinct protein composition and performing distinct functions (Chege and Pfeffer, 1990 ; Farquhar and Palade, 1981; Klausner, 1989; Pelham, 1991 ; Pfeffer and Rothman, 1987) . Generally, the Golgi apparatus can be further divided into the cis-Golgi network (Duden et al ., 1991 ; Hsu et al ., 1991; Pelham, 1991), the cis-, medial-, and trams-Golgi cisternae, as well as the transGolgi network (TGN)' (Grifliths and Simons, 1986) . Proteins in transport vesicles derived from the ER enter the Golgi apparatus from the cis-Golgi network, are transported along the cis-, medial-, and trans-Golgi cisternae through a series of vesicular intermediates, and exit the Golgi apparatus from the TGN. The Golgi apparatus performs a crucial role in protein sorting or targeting in both the exocytotic pathways (Dahms et al ., 1989 ; Hsu et aí.,1991 ; Kornfeld and Mellman, 1989 ; Orci et al ., 1987; Pelham, 1988, 1991; Rodriguez-Boulan and Nelson, 1989; Simons and WandingerNess, 1990 ; Tooze et al ., 1987; Vaux et al ., 1990) and the endocytotic pathways (Green and Kelly, 1990 ; Snider and Rogers, 1985 ; Woods et al ., 1986) . Several proteins have been localized to distinct subcompartments of the Golgi apparatus (Kornfeld and Kornfeld, 1985; Kornfeld and Mellman, 1989 ; Lewis and Pelham, 1990 ; Pelham, 1991 ; Saraste et al ., 1987 ; Schweizer et al ., 1988) . N-Acetylglucosaminyl1 . Abbreviations used in this paper : DPPIV, dipeptidyl peptidase IV; ECA, Erythrina cristagalli ; endo H, Endoglycosidase H ; GT, ß,l,4-galactosyltransferase ; MAA, Maackia amurensis; NTI, N-acetylglucosatninyltransferase 1 ; PBSCM, PBS with 1 mM CaC12 and 1 MM MgCl2 ; PCR, polymerase chain reaction ; SNA, Sambucus nigra ; ST, a2,6-sialyltransferase; sVIGA, succinylated wheat germ agglutinin ; TGN, trams-Golgi network; WGA, wheat germ agglutinin. © The Rockefeller University Press, 0021-9525/92/04/245/14 $2 .00 The Journal of Cell Biology, Volume 117, Number 2, April 1992 245-258 tegral membrane protein . Lectin affinity chromatography of chimeric proteins bearing this 17-residue sequence suggests that these chimeric proteins are localized in the trans-Golgi cisternae and/or trans-Golgi network. Further experiments suggest that this 17-residue sequence functions as a retention signal for the