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Vol. 17, Issue 2, 917-930, February 2006

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Seventeen a-Subunit Isoforms of Paramecium V-ATPase Provide High Specialization in Localization and Function

Thomas Wassmer ^* , Roland Kissmehl , Jean Cohen ^*, and Helmut Plattner 

^* Centre de Génétique Moleculaire, Centre National de la Recherche Scientifique, F-91198 Gif-sur-Yvette Cedex, France; Fachbereich Biologie, Universität Konstanz, D-78457 Konstanz, Germany

Submitted June 8, 2005; Revised November 8, 2005; Accepted November 14, 2005
Monitoring Editor: Howard Riezman

In the Paramecium tetraurelia genome, 17 genes encoding the 100-kDa-subunit (a-subunit) of the vacuolar-proton-ATPase were identified, representing by far the largest number of a-subunit genes encountered in any organism investigated so far. They group into nine clusters, eight pairs with >82% amino acid identity and one single gene. Green fluorescent protein-tagging of representatives of the nine clusters revealed highly specific targeting to at least seven different compartments, among them dense core secretory vesicles (trichocysts), the contractile vacuole complex, and phagosomes. RNA interference for two pairs confirmed their functional specialization in their target compartments: silencing of the trichocyst-specific form affected this secretory pathway, whereas silencing of the contractile vacuole complex-specific form altered organelle structure and functioning. The construction of chimeras between selected a-subunits surprisingly revealed the targeting signal to be located in the C terminus of the protein, in contrast with the N-terminal targeting signal of the a-subunit in yeast. Interestingly, some chimeras provoked deleterious effects, locally in their target compartment, or remotely, in the compartment whose specific a-subunit N terminus was used in the chimera.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Present address: Universität Konstanz, Universitätsstraße 10, D-78457 Konstanz, Germany.

Address correspondence to: Thomas Wassmer (thomas.wassmer{at}uni-konstanz.de).

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