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Functional characterization of class I Arfs and their Guanine Nucleotide Exchange Factors at the Golgi complex Open Access


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Type of item
Degree grantor
University of Alberta
Author or creator
Manolea, Florin Iulian
Supervisor and department
Dr. Paul Melançon (Department of Cell Biology)
Examining committee member and department
Dr. Tom Hobman, Department of Cell Biology, University of Alberta
Dr. Johnny K. Ngsee, Department of Medicine, University of Ottawa
Dr. Richard Lehner, Department of Cell Biology, University of Alberta
Dr. Zhixiang Wang, Department of Cell Biology, University of Alberta
Department of Cell Biology

Date accepted
Graduation date
Doctor of Philosophy
Degree level
We examined the function of ADP-ribosylation factors (Arfs) and their guanine nucleotide exchange factors (GEFs) that regulate recruitment of coat proteins on the Golgi complex. The large ArfGEF GBF1 localizes at the cis-Golgi complex while BIG1 and BIG2 localize at the trans-Golgi network (TGN). Complementary overexpression and RNA-based knockdown approaches established that GBF1 but not BIGs, is required for COPI recruitment, Golgi stack maintenance and sub-compartmentalization while BIGs appear specialized for clathrin adaptor recruitment and for assembly and maintenance of the TGN. Our observations disprove two widely accepted mechanisms for cargo export by establishing that COPII is the only coat required for sorting and export from the ER exit sites and that BIGs are not required for traffic of the cargo protein VSVG to the cell surface. Furthermore, we provide evidence that may ultimately explain how these ArfGEFs regulate different coats in spite of their well-characterized promiscuity towards class I and II Arfs. We prove for the first time that Arf3 is activated uniquely by BIGs at the TGN. Also, contrary to expectations, we demonstrate that Arf3 differs from Arf1 in regard to localization pattern as well as temperature sensitivity of membrane recruitment. Shifting temperature to 20ºC for 2 hours, a method known to block cargo in trans-Golgi compartments, caused a dramatic redistribution Arf3 but not Arf1. Redistribution of Arf3 from Golgi membranes upon shift to 20ºC was not immediate but occurred gradually over 20 minutes. Arf1 and Arf3 differ in sequence only in two short regions at the N- and C-termini. Analysis of swap constructs established that two amino acids in the N-terminal region of Arf3 and Arf1 are responsible for directing the temperature sensitivity while two amino acids in the C-terminus directs Arf3’s specific localization. Arf3 knockdown had no impact on any of the markers tested or on VSVG trafficking to the cell surface. My work provides solid evidence to support that ArfGEFs function at different compartments to regulate membrane recruitment of specific coat proteins, and may also regulate distinct sets of Arfs that localize preferentially to these particular compartments.
License granted by Florin Manolea ( on 2009-10-02T01:31:42Z (GMT): Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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