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J. Bacteriol., 07 1996, 4047-4051, Vol 178, No. 14
Copyright © 1996, American Society for Microbiology

A truncated form of the Pho80 cyclin of Saccharomyces cerevisiae induces expression of a small cytosolic factor which inhibits vacuole inheritance

T Nicolson, B Conradt and W Wickner
Molecular Biology Institute and Department of Biological Chemistry, University of Los Angeles, California 90024, USA.

Vacuoles project streams of vesicles and membranous tubules into the yeast bud where they fuse, founding the daughter cell organelle, vac5- 1, which encodes a truncated form of the Pho80 cyclin, inhibits normal vacuole inheritance. An in vitro inheritance assay which measures the fusion of vacuoles serves as a model for several steps of this process. We find that cytosol isolated from the vac5-1 mutant is unable to promote the fusion of wild-type vacuoles in the in vitro assay. Wild- type vacuoles are irreversibly inactivated in a time- and temperature- dependent manner if preincubated with vac5-1 cytosol and ATP, suggesting the presence of a soluble inhibitory factor. When mixed with wild-type cytosol, vac5-1 cytosol inhibits the activity of wild-type cytosol. vac5-1 cytosol treated with trypsin or papain is still able to inhibit the activity of Aid-type cytosol. Partial fractionation of vac5- 1 cytosol reveals that the protein traction (G25 void volume) can promote fusion if wild-type small molecules are included in the fusion reaction. In contrast, the vac5-l small-molecule fraction retains the full ability to inhibit fusion. Thus, the vac5-1 allele of PHO80 induces the synthesis of a small molecule that is an inhibitor of vacuole inheritance.

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• Bryant, N. J., Stevens, T. H. (1998). Vacuole Biogenesis in Saccharomyces cerevisiae: Protein Transport Pathways to the Yeast Vacuole. Microbiol. Mol. Biol. Rev. 62: 230-247 [Abstract] [Full Text]  
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