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A more recent version of this article appeared on August 1, 2004
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Submitted on March 12, 2004
Revised on May 6, 2004
Accepted on May 18, 2004
Department of Cellular and Molecular Medicine and the Howard Hughes Medical Institute, School of Medicine, University of California at San Diego, La Jolla, California 92093-0668
Monitoring Editor: Suzanne Pfeffer
The requirement of Vps34p, the sole phosphatidylinositol (PI) 3-kinase in S. cerevisiae, for protein sorting to the vacuole in yeast has exemplified the essential role for phosphoinositides, phosphorylated derivatives of PI, in membrane trafficking. To better understand mechanisms that regulate PI 3' phosphate (PI(3)P)-mediated signaling, the role of Ymr1p, the yeast myotubularin-related PI(3)P phosphatase was investigated. We found that Ymr1p and the synaptojanin-like phosphatase Sjl3p function as key regulators of the localization and levels of PI(3)P. Our data indicated that the ymr1
sjl3
double mutant aberrantly accumulated PI(3)P and demonstrated a steady-state redistribution of this lipid that leads to enrichment on the vacuolar membrane. This resulted in vacuole protein sorting defects, vacuolar fragmentation, and the mis-regulation of PI(3)P-specific effectors. Triple deletion of YMR1, SJL2, and SJL3 was lethal, suggesting an essential requirement for phosphatase-mediated PI(3)P regulation. Consistent with this, growth was restored to a ymr1
sjl2
sjl3
triple mutant by a PI(3)P-targeted Sac1p domain chimera (GFP-SacI
C-FYVEEEA1) that returned PI(3)P to levels comparable to wildtype cells. Taken together, this study demonstrated that Ymr1p, a myotubularin phosphatase family member, functions in the control of PI(3)P-dependent signaling, and the maintenance of endosomal system integrity. In addition, this work defined an essential overlapping role for lipid phosphatases in the regulation of 3' phosphoinositides in yeast.
*Corresponding author.
Scott D. Emr, E-mail: semr{at}ucsd.edu
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