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Publication Title

Proceedings of the National Academy of Sciences of the United States of America


Geisel School of Medicine


Vacuole fusion occurs in three stages: priming, in which Sec18p mediates Sec17p release, LMA1 (low Mr activity 1) relocation, and cis-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex disassembly; docking, mediated by Ypt7p and trans-SNARE association; and fusion of docked vacuoles. Ca2+ and calmodulin regulate late stages of the reaction. We now show that the vacuole proton gradient, generated by the vacuolar proton ATPase, is needed for trans-SNARE complex formation during docking and hence for the subsequent LMA1 release. Though neither the vacuolar Pmc1p Ca2+-ATPase nor the Vcx1p Ca2+/H+ exchanger are needed for the fusion reaction, they participate in Ca2+ and ΔμH+ homeostasis. Fusion itself does not require the maintenance of trans-SNARE pairs.



Original Citation

Ungermann C, Wickner W, Xu Z. Vacuole acidification is required for trans-SNARE pairing, LMA1 release, and homotypic fusion. Proc Natl Acad Sci U S A. 1999;96(20):11194-11199. doi:10.1073/pnas.96.20.11194