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Eukaryotic Cell, March 2009, p. 278-286, Vol. 8, No. 3
1535-9778/09/$08.00+0     doi:10.1128/EC.00363-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Dual Sorting of the Saccharomyces cerevisiae Vacuolar Protein Sna4p {triangledown}

W. Pokrzywa,{dagger} B. Guerriat,{dagger} J. Dodzian, and P. Morsomme*

Université Catholique de Louvain, Institut des Sciences de la Vie, Unité de Biochimie Physiologique, Place Croix du Sud 5/15, B-1348 Louvain-La-Neuve, Belgium

Received 10 November 2008/ Accepted 28 December 2008

Sna4p, a vacuolar membrane protein, belongs to a small family of proteins conserved in plants and fungi. It is transported to the vacuolar membrane via the alkaline phosphatase (ALP) pathway, which bypasses the multivesicular bodies (MVBs). Here, we show that transfer of Sna4p by the ALP route involves the AP-3 adaptor protein complex, which binds to an acidic dileucine sorting signal in the cytoplasmic region of Sna4p. In addition, Sna4p can use the MVB pathway by using a PPPY motif, which is involved in the interaction with ubiquitin ligase Rsp5p. Deletion or mutation of the Sna4p PPPY motif or a low level of Rsp5p inhibits the entrance of Sna4p into MVBs. Sna4p is polyubiquitylated on its only lysine, and Sna4p lacking this lysine shows defective MVB sorting. These data indicate that Sna4p has two functional motifs, one for interaction with the AP-3 complex, followed by entry into the ALP pathway, and one for binding Rsp5p, which directs the protein to the MVB pathway. The presence of these two motifs allows Sna4p to localize to both the vacuolar membrane and the lumen.

* Corresponding author. Mailing address: Université Catholique de Louvain, Institut des Sciences de la Vie, Unité de Biochimie Physiologique, Place Croix du Sud 5/15, B-1348 Louvain-La-Neuve, Belgium. Phone: 32 10 47 26 23. Fax: 32 10 47 38 72. E-mail: pierre.morsomme{at}uclouvain.be

{triangledown} Published ahead of print on 23 January 2009.

{dagger} These authors contributed equally to this work.

Eukaryotic Cell, March 2009, p. 278-286, Vol. 8, No. 3
1535-9778/09/$08.00+0     doi:10.1128/EC.00363-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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