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Reference: Pina FJ, et al. (2011) Hph1 and hph2 are novel components of the sec63/sec62 posttranslational translocation complex that aid in vacuolar proton ATPase biogenesis. Eukaryot Cell 10(1):63-71

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Abstract

Hph1 and Hph2 are homologous integral ER-membrane proteins required for yeast survival under environmental stress conditions. To investigate the molecular functions of Hph1 and Hph2 we carried out a split-ubiquitin membrane-based yeast two-hybrid screen, and identified their interactions with Sec71, a subunit of the Sec63/Sec62 complex, which mediates post-translational translocation of proteins into the ER. Hph1 and Hph2 likely function in post-translational translocation, as they interact with other Sec63/Sec62 complex subunits, i.e. Sec72, Sec62, and Sec63. hph1Delta hph2Delta cells display reduced vacuole acidification, increased instability of Vph1, a subunit of the V-ATPase, and growth defects similar to those of mutants lacking vacuolar proton ATPase (V-ATPase) activity. sec71Delta cells exhibit similar phenotypes, indicating that Hph1/Hph2 and the Sec63/Sec62 complex function during V-ATPase biogenesis. Hph1/Hph2 and the Sec63/Sec62 complex may act together in this process, as vacuolar acidification and Vph1 stability are compromised to the same extent in hph1Delta hph2Delta and hph1Delta hph2Delta sec71Delta cells. In contrast, loss of Pkr1, an ER protein that promotes post-translocation assembly of Vph1 with V-ATPase subunits, further exacerbates hph1Delta hph2Delta phenotypes, suggesting that Hph1 and Hph2 function independently of Pkr1-mediated V-ATPase assembly. We propose that Hph1 and Hph2 aid Sec63/Sec62-mediated translocation of specific proteins, including factors that promote efficient biogenesis of the V-ATPase, to support yeast cell survival during environmental stress.

Reference Type
Journal Article
Authors
Pina FJ, O'Donnell AF, Pagant S, Piao HL, Miller JP, Fields S, Miller EA, Cyert MS
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