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Molecular and Cellular Biology, July 2002, p. 4914-4928, Vol. 22, No. 13
0270-7306/02/$04.00+0     DOI: 10.1128/MCB.22.13.4914-4928.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

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

Alexandra Jochum,1 David Jackson,2 Heinz Schwarz,3 Rüdiger Pipkorn,4 and Birgit Singer-Krüger1*

Institute for Biochemistry, University of Stuttgart, D-70569 Stuttgart,1 Lion Bioscience,2 Deutsches Krebsforschungszentrum, D-69120 Heidelberg,4 Max-Planck Institute for Developmental Biology, D-72076 Tübingen, Germany3

Received 17 January 2002/ Returned for modification 14 February 2002/ Accepted 9 April 2002

We previously described the isolation of ysl2-1 due to its genetic interaction with {Delta}ypt51/vps21, a mutant with a deletion of the coding sequence for the yeast Rab5 homolog, which regulates endocytic traffic between early and late endosomes. Here we report that Ysl2p is a novel 186.8-kDa peripheral membrane protein homologous to members of the Sec7 family. We provide multiple genetic and biochemical evidence for an interaction between Ysl12p and the Arf-like protein Arl1p, consistent with a potential function as an Arf guanine nucleotide exchange factor (GEF). The temperature-sensitive alleles ysl2-307 and ysl2-316 are specifically defective in ligand-induced degradation of Ste2p and {alpha}-factor and exhibit vacuole fragmentation directly upon a shift to 37°C. In living cells, green fluorescent protein (GFP)-Ysl2p colocalizes with endocytic elements that accumulate FM4-64. The GFP-Ysl2p staining is sensitive to a mutation in VPS27 resulting in the formation of an aberrant class E compartment, but it is not affected by a sec7 mutation. Consistent with the idea that Ysl2p and Arl1p have closely related functions, {Delta}arl1 cells are defective in endocytic transport and in vacuolar protein sorting.

* Corresponding author. Mailing address: Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany. Phone: 049-711-685-4387. Fax: 049-711-685-4392. E-mail: Singer-Krueger{at}po.uni-stuttgart.de.

Molecular and Cellular Biology, July 2002, p. 4914-4928, Vol. 22, No. 13
0022-538X/02/$04.00+0     DOI: 10.1128/MCB.22.13.4914-4928.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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