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Updated: Jan 30, 2026

Identification of Host Pathways Targeted by Bacterial Effector Proteins using Yeast Toxicity and Suppressor Screens
Published on: October 25, 2019
Rab5-independent activation and function of yeast Rab7-like protein, Ypt7p, in the AP-3 pathway
Hiroki Shimamura1, Makoto Nagano1, Keita Nakajima1
1Department of Biological Science and Technology, Tokyo University of Science, Niijyuku, Katsushika-ku, Tokyo, Japan.
Abstract:
The small GTPases, Rab5 and Rab7, are key regulators at multiple stages of the endocytic/endolysosomal pathway, including fusion and maturation of endosomes. In yeast, Vps21p (Rab5 homolog) recruits a GEF for Rab7 and activates the downstream Ypt7p (Rab7 homolog) on endosomal membrane. Although the model of this sequential activation from Vps21p to Ypt7p in the endocytic pathway has been established, activation mechanism of Ypt7p in the Vps21p-independent pathway has not been completely clarified. Here we show that Ypt7p is activated and mediates vacuolar fusion in cells lacking all yeast Rab5 genes, VPS21, YPT52, and YPT53. We also demonstrate that deletion of both VPS21 and YPT7 genes cause severe defect in the AP-3 pathway as well as the CPY pathway although the AP-3 pathway is mostly intact in each vps21Δ or ypt7Δ mutant. Interestingly, in vps21Δ ypt7Δ mutant cargos trafficked via the VPS or endocytic pathway accumulate beside nucleus whereas cargo trafficked via the AP-3 pathway disperse in the cytosol. These findings suggest that Ypt7p is activated and plays a Rab5-independent role in the AP-3-mediated pathway.
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