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Vol. 17, Issue 12, 5153-5162, December 2006
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Institute of Physiology, University of Zurich, CH-8057 Zurich, Switzerland
Submitted August 2, 2006;
Revised September 13, 2006;
Accepted September 27, 2006
Monitoring Editor: Vivek Malhotra
The Golgi apparatus (GA) is the organelle where complex glycan formation takes place. In addition, it is a major sorting site for proteins destined for various subcellular compartments or for secretion. Here we investigate
1,4-galactosyltransferase 1 (galT) and
2,6-sialyltransferase 1 (siaT), two trans-Golgi glycosyltransferases, with respect to their different pathways in monensin-treated cells. Upon addition of monensin galT dissociates from siaT and the GA and accumulates in swollen vesicles derived from the trans-Golgi network (TGN), as shown by colocalization with TGN46, a specific TGN marker. We analyzed various chimeric constructs of galT and siaT by confocal fluorescence microscopy and time-lapse videomicroscopy as well as Optiprep density gradient fractionation. We show that the first 13 amino acids of the cytoplasmic tail of galT are necessary for its localization to swollen vesicles induced by monensin. We also show that the monensin sensitivity resulting from the cytoplasmic tail can be conferred to siaT, which leads to the rapid accumulation of the galTsiaT chimera in swollen vesicles upon monensin treatment. On the basis of these data, we suggest that cycling between the trans-Golgi cisterna and the trans-Golgi network of galT is signal mediated.
This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E06-08-0665) on October 4, 2006.
Address correspondence to: Jack Rohrer (rohrer.jack{at}access.unizh.ch)
Abbreviations used: galT,
1,4-galactosyltransferase 1; siaT,
2,6-sialyltransferase 1; GA, Golgi apparatus; TGN, trans-Golgi network; ER, endoplasmic reticulum; BFA, brefeldin A; ECL, enhanced chemiluminescence.
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