Abstract
Many of the vacuolar protein sorting (vps) mutants of Saccharomyces cerevisiae exhibit severe defects in the sorting of vacuolar proteins but still retain near-normal vacuole morphology. The gene affected in one such mutant, vps21, has been cloned and found to encode a member of the ras-like GTP binding protein family. Sequence comparisons with other known GTP binding proteins indicate that Vps21p is unique but shares striking similarity with mammalian rab5 proteins (> 50% identity and >70% similarity). Regions with highest similarity are clustered within the putative GTP binding motifs and the proposed effector domains of the Vps21/rab5 proteins. Point mutations constructed within these conserved regions inactivate Vps21p function; the mutant cells missort and secrete the soluble vacuolar hydrolase carboxypeptidase Y (CPY). Cells carrying a complete deletion of the VPS21 coding sequence (i) are viable but exhibit a growth defect at 38°C, (ii) missort multiple vacuolar proteins, (iii) accumulate 40-50 nm vesicles and (iv) contain a large vacuole. VPS21 encodes a 22 kDa protein that binds GTP and fractionates with subcellular membranes. Mutant analysis indicates that the association with a membrane(s) is dependent on geranylgeranylation of the C-terminal cysteine residue(s) of Yps21p. We propose that Vps21p functions in the targeting and/or fusion of transport vesicles that mediate the delivery of proteins to the vacuole.
Original language | English (US) |
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Pages (from-to) | 1297-1309 |
Number of pages | 13 |
Journal | EMBO Journal |
Volume | 13 |
Issue number | 6 |
DOIs | |
State | Published - Mar 15 1994 |
Keywords
- GTP binding protein
- Sorting
- VPS21
- Vacuole
- Yeast
ASJC Scopus subject areas
- General Neuroscience
- Molecular Biology
- General Biochemistry, Genetics and Molecular Biology
- General Immunology and Microbiology