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Molecular and Cellular Biology, November 2009, p. 5975-5988, Vol. 29, No. 22
0270-7306/09/$08.00+0     doi:10.1128/MCB.00069-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Genetic and Functional Interactions between the Mitochondrial Outer Membrane Proteins Tom6 and Sam37{triangledown}

Jovana Dukanovic,1 Kai S. Dimmer,1 Nathalie Bonnefoy,2 Katrin Krumpe,1 and Doron Rapaport1*

Interfaculty Institute for Biochemistry, Hoppe-Seyler-Str. 4, University of Tübingen, 72076 Tübingen, Germany,1 Centre de Génétique Moléculaire, CNRS FRE3144, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France2

Received 16 January 2009/ Returned for modification 17 February 2009/ Accepted 8 September 2009

The TOM complex is the general mitochondrial entry site for newly synthesized proteins. Precursors of β-barrel proteins initially follow this common pathway and are then relayed to the SAM/TOB complex, which mediates their integration into the outer membrane. Three proteins, Sam50 (Tob55), Sam35 (Tob38/Tom38), and Sam37 (Mas37), have been identified as the core constituents of the latter complex. Sam37 is essential for growth at elevated temperatures, but the function of the protein is currently unresolved. To identify interacting partners of Sam37 and thus shed light on its function, we screened for multicopy suppressors of sam37{Delta}. We identified the small subunit of the TOM complex, Tom6, as such a suppressor and found a tight genetic interaction between the two proteins. Overexpression of SAM37 suppresses the growth phenotype of tom6{Delta}, and cells lacking both genes are not viable. The ability of large amounts of Tom6 to suppress the sam37{Delta} phenotype can be linked to the capacity of Tom6 to stabilize Tom40, an essential β-barrel protein which is the central component of the TOM complex. Our results suggest that Sam37 is required for growth at higher temperatures, since it enhances the biogenesis of Tom40, and this requirement can be overruled by improved stability of newly synthesized Tom40 molecules.

* Corresponding author. Mailing address: Interfaculty Institute for Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076 Tübingen, Germany. Phone: 49-7071-2974184. Fax: 49-7071-295565. E-mail: doron.rapaport{at}uni-tuebingen.de

{triangledown} Published ahead of print on 21 September 2009.

Molecular and Cellular Biology, November 2009, p. 5975-5988, Vol. 29, No. 22
0270-7306/09/$08.00+0     doi:10.1128/MCB.00069-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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