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Multiple classes of yeast mutants are defective in vacuole partitioning yet target vacuole proteins correctly
Y X Wang1, H Zhao, T M Harding
1Department of Biochemistry, University of Iowa, Iowa City 52242, USA.
Abstract:
In Saccharomyces cerevisiae the vacuoles are partitioned from mother cells to daughter cells in a cell-cycle-coordinated process. The molecular basis of this event remains obscure. To date, few yeast mutants had been identified that are defective in vacuole partitioning (vac), and most such mutants are also defective in vacuole protein sorting (vps) from the Golgi to the vacuole. Both the vps mutants and previously identified non-vps vac mutants display an altered vacuolar morphology. Here, we report a new method to monitor vacuole inheritance and the isolation of six new non-vps vac mutants. They define five complementation groups (VAC8-VAC12). Unlike mutants identified previously, three of the complementation groups exhibit normal vacuolar morphology. Zygote studies revealed that these vac mutants are also defective in intervacuole communication. Although at least four pathways of protein delivery to the vacuole are known, only the Vps pathway seems to significantly overlap with vacuole partitioning. Mutants defective in both vacuole partitioning and endocytosis or vacuole partitioning and autophagy were not observed. However, one of the new vac mutants was additionally defective in direct protein transport from the cytoplasm to the vacuole.
Insights
Researchers identified new yeast mutants defective in vacuole partitioning, a cell-cycle process crucial for inheritance. Some mutants show normal vacuole shape but impaired intervacuole communication, revealing new insights into this essential cellular event.
Area of Science:
- Cell Biology
- Yeast Genetics
Background:
- Vacuole partitioning is a cell-cycle-coordinated process in Saccharomyces cerevisiae, essential for inheritance but poorly understood.
- Previous studies identified vacuole partitioning (vac) mutants, often also defective in vacuole protein sorting (vps) and exhibiting altered vacuole morphology.
Purpose of the Study:
- To develop a new method for monitoring vacuole inheritance.
- To isolate and characterize novel non-vps mutants defective in vacuole partitioning.
Main Methods:
- Isolation and complementation analysis of six new non-vps vac mutants.
- Monitoring vacuole inheritance using a novel method.
- Morphological analysis of vacuoles.
- Zygote studies to assess intervacuole communication.
Main Results:
- Six new non-vps vac mutants were isolated, defining five complementation groups (VAC8-VAC12).
- Three complementation groups displayed normal vacuole morphology, unlike previously identified mutants.
- These three mutants were also defective in intervacuole communication.
- One mutant showed a defect in direct protein transport from the cytoplasm to the vacuole.
Conclusions:
- Vacuole partitioning involves complex mechanisms beyond vacuole protein sorting.
- Impaired intervacuole communication is a key feature in some vacuole partitioning defects.
- New pathways and genetic interactions in vacuole inheritance are uncovered.