A role for ubiquitin in the cytosol to vacuole trafficking pathway.
Bonnie Baxter (1), Hagai Abeliovich (2), David Goldfarb (1)
(1) Department of Biology, University of Rochester, 435 Hutchison Hall, Rochester, NY, 14627, USA;
(2) Hebrew University of Jerusalem, Faculty of Agriculture, P.O.B. 12, Rehovot, 76100 Israel
Atg19 is the cargo receptor protein in the cytosol to vacuole trafficking (Cvt) pathway, required for the specific transport of aminopeptidase I and alpha-mannosidase I to the vacuole. Atg19 travels with its cargo to the vacuole, where the cargo proteins function and Atg19 is degraded. We isolated Atg19 as an interactor of the de-ubiquitinating protein Ubp3 in a two-hybrid screen. This is the first finding to suggest a role for ubiquitin in the Cvt pathway. We show that Atg19 and Ubp3 interact specifically both in the two hybrid system and in biochemical pulldown assays. Atg19 is ubiquitinated in vivo on two centrally-located lysine residues, and ubiquitinated Atg19 accumulates in ubp3-delta cells. A functional role for Atg19 de-ubiquitination is suggested by the finding that ubp3-delta cells show delayed processing of the Cvt cargo protein aminipeptidase I. These data are consistent with a role for reversible ubiquitination either as a requirement for Atg19 function or as a regulatory mechanism for its proteasomal destruction. Experiments designed to distinguish between these two possibilities will be presented.
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