Genetic Interactions in Yeast Between Ypt GTPases and Arf Guanine Nucleotide Exchangers

Corresponding author: Nava Segev, Department of Pharmacological and Physiological Sciences, The University of Chicago, 947 E. 58th Street, Chicago, IL 60637., ns15{at}midway.uchicago.edu (E-mail)

Communicating editor: E. W. JONES

Two families of GTPases, Arfs and Ypt/rabs, are key regulators of vesicular transport. While Arf proteins are implicated in vesicle budding from the donor compartment, Ypt/rab proteins are involved in the targeting of vesicles to the acceptor compartment. Recently, we have shown a role for Ypt31/32p in exit from the yeast trans-Golgi, suggesting a possible function for Ypt/rab proteins in vesicle budding as well. Here we report the identification of a new member of the Sec7-domain family, SYT1, as a high-copy suppressor of a ypt31/32 mutation. Several proteins that belong to the Sec7-domain family, including the yeast Gea1p, have recently been shown to stimulate nucleotide exchange by Arf GTPases. Nucleotide exchange by Arf GTPases, the switch from the GDP- to the GTP-bound form, is thought to be crucial for their function. Sec7p itself has an important role in the yeast secretory pathway. However, its mechanism of action is not yet understood. We show that all members of the Sec7-domain family exhibit distinct genetic interactions with the YPT genes. Biochemical assays demonstrate that, although the homology between the members of the Sec7-domain family is relatively low (20–35%) and limited to a small domain, they all can act as guanine nucleotide exchange factors (GEFs) for Arf proteins, but not for Ypt GTPases. The Sec7-domain of Sec7p is sufficient for this activity. Interestingly, the Sec7 domain activity is inhibited by brefeldin A (BFA), a fungal metabolite that inhibits some of the Arf-GEFs, indicating that this domain is a target for BFA. These results demonstrate that the ability to act as Arf-GEFs is a general property of all Sec7-domain proteins in yeast. The genetic interactions observed between Arf GEFs and Ypt GTPases suggest the existence of a Ypt-Arf GTPase cascade in the secretory pathway.

This article has been cited by other articles:

				P. Monetta, I. Slavin, N. Romero, and C. Alvarez Rab1b Interacts with GBF1 and Modulates both ARF1 Dynamics and COPI Association Mol. Biol. Cell, July 1, 2007; 18(7): 2400 - 2410. [Abstract] [Full Text] [PDF]

				V. A. Sciorra, A. Audhya, A. B. Parsons, N. Segev, C. Boone, and S. D. Emr Synthetic Genetic Array Analysis of the PtdIns 4-kinase Pik1p Identifies Components in a Golgi-specific Ypt31/rab-GTPase Signaling Pathway Mol. Biol. Cell, February 1, 2005; 16(2): 776 - 793. [Abstract] [Full Text] [PDF]

				M. Trautwein, J. Dengjel, M. Schirle, and A. Spang Arf1p Provides an Unexpected Link between COPI Vesicles and mRNA in Saccharomyces cerevisiae Mol. Biol. Cell, November 1, 2004; 15(11): 5021 - 5037. [Abstract] [Full Text] [PDF]

				R. Cox, R. J Mason-Gamer, C. L. Jackson, and N. Segev Phylogenetic Analysis of Sec7-Domain-containing Arf Nucleotide Exchangers Mol. Biol. Cell, April 1, 2004; 15(4): 1487 - 1505. [Abstract] [Full Text] [PDF]

				E. Zakrzewska, M. Perron, A. Laroche, and D. Pallotta A Role for GEA1 and GEA2 in the Organization of the Actin Cytoskeleton in Saccharomyces cerevisiae Genetics, November 1, 2003; 165(3): 985 - 995. [Abstract] [Full Text] [PDF]

				S. Chantalat, R. Courbeyrette, F. Senic-Matuglia, C. L. Jackson, B. Goud, and A. Peyroche A Novel Golgi Membrane Protein Is a Partner of the ARF Exchange Factors Gea1p and Gea2p Mol. Biol. Cell, June 1, 2003; 14(6): 2357 - 2371. [Abstract] [Full Text] [PDF]

				C. Alvarez, R. Garcia-Mata, E. Brandon, and E. Sztul COPI Recruitment Is Modulated by a Rab1b-dependent Mechanism Mol. Biol. Cell, May 1, 2003; 14(5): 2116 - 2127. [Abstract] [Full Text] [PDF]

				M. P. Washburn, A. Koller, G. Oshiro, R. R. Ulaszek, D. Plouffe, C. Deciu, E. Winzeler, and J. R. Yates III Protein pathway and complex clustering of correlated mRNA and protein expression analyses in Saccharomycescerevisiae PNAS, March 18, 2003; 100(6): 3107 - 3112. [Abstract] [Full Text] [PDF]

				A. Jochum, D. Jackson, H. Schwarz, R. Pipkorn, and B. Singer-Kruger Yeast Ysl2p, Homologous to Sec7 Domain Guanine Nucleotide Exchange Factors, Functions in Endocytosis and Maintenance of Vacuole Integrity and Interacts with the Arf-Like Small GTPase Arl1p Mol. Cell. Biol., July 1, 2002; 22(13): 4914 - 4928. [Abstract] [Full Text] [PDF]

				D. Ortiz, M. Medkova, C. Walch-Solimena, and P. Novick Ypt32 recruits the Sec4p guanine nucleotide exchange factor, Sec2p, to secretory vesicles; evidence for a Rab cascade in yeast J. Cell Biol., June 10, 2002; 157(6): 1005 - 1016. [Abstract] [Full Text] [PDF]

				E. S. Suvorova, R. Duden, and V. V. Lupashin The Sec34/Sec35p complex, a Ypt1p effector required for retrograde intra-Golgi trafficking, interacts with Golgi SNAREs and COPI vesicle coat proteins J. Cell Biol., May 13, 2002; 157(4): 631 - 643. [Abstract] [Full Text] [PDF]

				A. Peyroche, R. Courbeyrette, A. Rambourg, and C. L. Jackson The ARF exchange factors Gea1p and Gea2p regulate Golgi structure and function in yeast J. Cell Sci., March 8, 2002; 114(12): 2241 - 2253. [Abstract] [Full Text] [PDF]

				H. Nagai, J. C. Kagan, X. Zhu, R. A. Kahn, and C. R. Roy A Bacterial Guanine Nucleotide Exchange Factor Activates ARF on Legionella Phagosomes Science, January 25, 2002; 295(5555): 679 - 682. [Abstract] [Full Text] [PDF]

				N. Segev Ypt/Rab GTPases: Regulators of Protein Trafficking Sci. Signal., September 18, 2001; 2001(100): re11 - re11. [Abstract] [Full Text] [PDF]

				A. Spang, J. M. Herrmann, S. Hamamoto, and R. Schekman The ADP Ribosylation Factor-Nucleotide Exchange Factors Gea1p and Gea2p Have Overlapping, but Not Redundant Functions in Retrograde Transport from the Golgi to the Endoplasmic Reticulum Mol. Biol. Cell, April 1, 2001; 12(4): 1035 - 1045. [Abstract] [Full Text]

				N. Yahara, T. Ueda, K. Sato, and A. Nakano Multiple Roles of Arf1 GTPase in the Yeast Exocytic and Endocytic Pathways Mol. Biol. Cell, January 1, 2001; 12(1): 221 - 238. [Abstract] [Full Text]

				J Somsel Rodman and A Wandinger-Ness Rab GTPases coordinate endocytosis J. Cell Sci., January 1, 2000; 113(2): 183 - 192. [Abstract] [PDF]