VMA12 Encodes a Yeast Endoplasmic Reticulum Protein Required for Vacuolar H+-ATPase Assembly*

  title={VMA12 Encodes a Yeast Endoplasmic Reticulum Protein Required for Vacuolar H+-ATPase Assembly*},
  author={D. Dewaine Jackson and Tom H. Stevens},
  journal={The Journal of Biological Chemistry},
  pages={25928 - 25934}
The Saccharomyces cerevisiae vacuolar membrane proton-translocating ATPase (V-ATPase) can be divided into a peripheral membrane complex (V1) containing at least eight polypeptides of 69, 60, 54, 42, 32, 27, 14, and 13 kDa, and an integral membrane complex (V0) containing at least five polypeptides of 100, 36, 23, 17, and 16 kDa. Other yeast genes have been identified that are required for V-ATPase assembly but whose protein products do not co-purify with the enzyme complex. One such gene,VMA12… 

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Composition and assembly of the yeast vacuolar H(+)-ATPase complex.
The proton-translocating ATPase (H(+)-ATPase) found on the membrane of the yeast vacuole is the best characterized member of the V-type ATPase family and 14 genes, the majority designated VMA (for vacuolar membrane ATPase) encoding subunits of the enzyme complex are identified.
Vma9p (Subunit e) Is an Integral Membrane V0 Subunit of the Yeast V-ATPase*
It is demonstrated that disruption of yeast VMA9 results in the failure of V1 and V0 V-ATPase subunits to assemble onto the vacuole and in decreased levels of the subunit a isoforms Vph1p and Stv1p, and suggested a model for the arrangement of polypeptides within the V0 subcomplex.
Assembly of the Yeast Vacuolar H+-ATPase Occurs in the Endoplasmic Reticulum and Requires a Vma12p/Vma22p Assembly Complex
Subcellular fractionation and chemical cross-linking studies have revealed that Vma12p and Vma22p form a stable membrane associated complex, the first evidence for a dedicated assembly complex in the ER required for the assembly of an integral membrane protein complex (V-ATPase) as it is transported through the secretory pathway.
Assembly of the Yeast Vacuolar Proton-Translocating ATPase
Three genes in yeast are identified that codefor proteins that are not part of the final V-ATPase complex yet required for its assembly, and these nonsubunit Vma proteins are referred to as assembly factors, since their function is dedicated to assembling the V- ATPase.
Role of Vma21p in assembly and transport of the yeast vacuolar ATPase.
It is concluded that Vma21p is not involved in regulating the interaction between V0 and V1 sectors, but that it has a crucial role in coordinating the assembly of V0 subunits and in escorting the assembled V0 complex into ER-derived transport vesicles.
Voa1p functions in V-ATPase assembly in the yeast endoplasmic reticulum.
A fifth V(0) assembly factor is discovered, Voa1p (YGR106C); an endoplasmic reticulum (ER)-localized integral membrane glycoprotein whose role was revealed in cells expressing an ER retrieval-deficient form of the V-ATPase assembly factor Vma21p (Vma 21pQQ).
A 100 kDa polypeptide associates with the V0 membrane sector but not with the active oat vacuolar H(+)-ATPase, suggesting a role in assembly.
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The absence of this polypeptide from the active enzyme suggests that, unlike the yeast Vph1p, the 100 kDa polypePTide in oat is not required for activity.
Early Steps in Assembly of the Yeast Vacuolar H+-ATPase*
The data suggest that in wild-type cells, assembly occurs predominantly by the concerted assembly pathway, and V-ATPase complexes acquire the full complement of Vosubunits during or after exit from the endoplasmic reticulum.
Structure and Assembly of the Yeast V-ATPase
The yeast V-ATPase belongs to a family of V-type ATPases present in all eucaryotic organisms and homologues of the Vma21p assembly factor have been identified in many higher eukaryotes supporting a ubiquitous assembly pathway for this important enzyme complex.
Functional complementation reveals that 9 of the 13 human V-ATPase subunits can functionally substitute for their yeast orthologs
Ass assessments revealed that 9 of the 13 human V-ATPase subunits can partially or fully complement the function of the corresponding yeast subunits, and sequence similarity was not necessarily correlated with functional complementation.


Vma22p Is a Novel Endoplasmic Reticulum-associated Protein Required for Assembly of the Yeast Vacuolar H+-ATPase Complex (*)
Results indicate that Vma22p, along with Vma21p and Vma12p, form a set of ER proteins required for V-ATPase assembly, which is associated with ER membranes.
Vma21p is a yeast membrane protein retained in the endoplasmic reticulum by a di-lysine motif and is required for the assembly of the vacuolar H(+)-ATPase complex.
It is suggested that Vma21p is required for assembly of the integral membrane sector of the V-ATPase in the endoplasmic reticulum and that the unassembled 100-kDa integral membrane subunit present in delta vma21 cells is rapidly degraded by nonvacuolar proteases.
VMA11 and VMA16 Encode Second and Third Proteolipid Subunits of the Saccharomyces cerevisiae Vacuolar Membrane H+-ATPase*
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