JCB logo
Accuri Cytometers
  Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents

This Article
Right arrow Full Text
Right arrow Full Text (PDF, 593K)
Right arrow PPT slides of all figures
Right arrow Alert me when this article is cited
Right arrow Citation Map
Services
Right arrow Email this article
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new content in the JCB
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via CrossRef
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Gary, J. D.
Right arrow Articles by Emr, S. D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Gary, J. D.
Right arrow Articles by Emr, S. D.
Social Bookmarking
 Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Facebook   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?

© The Rockefeller University Press, 0021-9525/1998//65 $5.00
The Journal of Cell Biology, Volume 143, Number 1, , 1998 65-79


Regular Articles

Fab1p Is Essential for PtdIns(3)P 5-Kinase Activity and the Maintenance of Vacuolar Size and Membrane Homeostasis



Jonathan D. Gary*, Andrew E. Wurmser*, Cecilia J. Bonangelino§, Lois S. Weisman§, and Scott D. Emr*

* Division of Cellular and Molecular Medicine and Howard Hughes Medical Institute, University of California at San Diego, School of Medicine, La Jolla, California 92093-0668; and § Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242

The Saccharomyces cerevisiae FAB1 gene encodes a 257-kD protein that contains a cysteine-rich RING-FYVE domain at its NH2-terminus and a kinase domain at its COOH terminus. Based on its sequence, Fab1p was initially proposed to function as a phosphatidylinositol 4-phosphate (PtdIns(4)P) 5-kinase (Yamamoto et al., 1995). Additional sequence analysis of the Fab1p kinase domain, reveals that Fab1p defines a subfamily of putative PtdInsP kinases that is distinct from the kinases that synthesize PtdIns(4,5)P2. Consistent with this, we find that unlike wild-type cells, fab1{Delta}, fab1tsf, and fab1 kinase domain point mutants lack detectable levels of PtdIns(3,5)P2, a phosphoinositide recently identified both in yeast and mammalian cells. PtdIns(4,5)P2 synthesis, on the other hand, is only moderately affected even in fab1{Delta} mutants. The presence of PtdIns(3)P in fab1 mutants, combined with previous data, indicate that PtdIns(3,5)P2 synthesis is a two step process, requiring the production of PtdIns(3)P by the Vps34p PtdIns 3-kinase and the subsequent Fab1p- dependent phosphorylation of PtdIns(3)P yielding PtdIns(3,5)P2. Although Vps34p-mediated synthesis of PtdIns(3)P is required for the proper sorting of hydrolases from the Golgi to the vacuole, the production of PtdIns(3,5)P2 by Fab1p does not directly affect Golgi to vacuole trafficking, suggesting that PtdIns(3,5)P2 has a distinct function. The major phenotypes resulting from Fab1p kinase inactivation include temperature-sensitive growth, vacuolar acidification defects, and dramatic increases in vacuolar size. Based on our studies, we hypothesize that whereas Vps34p is essential for anterograde trafficking of membrane and protein cargoes to the vacuole, Fab1p may play an important compensatory role in the recycling/turnover of membranes deposited at the vacuole. Interestingly, deletion of VAC7 also results in an enlarged vacuole morphology and has no detectable PtdIns(3,5)P2, suggesting that Vac7p functions as an upstream regulator, perhaps in a complex with Fab1p. We propose that Fab1p and Vac7p are components of a signal transduction pathway which functions to regulate the efflux or turnover of vacuolar membranes through the regulated production of PtdIns(3,5)P2.

Key Words: vacuole • lipid kinase • PtdIns(3,5)P2 VAC7VPS34



Abbreviations used in this paper: a.a., amino acid; ALP, alkaline phosphatase; API, aminopeptidase I; CPS, carboxypeptidase S; CPY, carboxypeptidase Y; G6PHD, glucose 6-phosphate dehydrogenase; PITP, PtdIns transfer protein; PtdIns(4)P, phosphatidylinositol 4-phosphate.

The first two authors contributed equally to this work.



Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Facebook Facebook   Add to Reddit Reddit   Add to Technorati Technorati   Add to Twitter Twitter    What's this?


This article has been cited by other articles:



  Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents