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J. Biol. Chem., Vol. 277, Issue 32, 28757-28764, August 9, 2002
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From the Department Biologie I, Bereich Genetik, Ludwig Maximilians
Universität München, Maria-Ward-Strasse 1a, D-80638 Munich,
Germany
Yeast adenylate kinase (Aky2p, Adk1p) occurs
simultaneously in cytoplasm and mitochondrial intermembrane space. It
has no cleavable mitochondrial targeting sequence, and the signal for mitochondrial import and submitochondrial sorting is largely unknown. The extreme N terminus of Aky2p is able to direct cytoplasmic passengers to mitochondria. However, an Aky2 mutant lacking this sequence is imported with about the same efficiency as the wild type. To identify possible import-relevant information in the interior,
parts of Aky2p were exchanged by homologous in vitro recombination for the respective segments of the purely cytoplasmic isozyme, Ura6p. Import studies revealed an internal region of about 40 amino acids, which was sufficient to direct the chimera to mitochondria
but not for correct submitochondrial sorting. The respective Ura6p
hybrid was arrested in the mitochondrial membrane at a position where
it was inaccessible to protease but was released by alkaline
extraction, suggesting that it had entered an import channel and passed
the initial steps of recognition and uptake. Site-specific mutations
within the presumptive address-specifying segment identified the
amphipathic helix 5. A Ura6 mutant protein in which helix 5 had
been replaced with the respective sequence from Aky2p was imported, and
this address sequence cooperates with the N terminus in the respective
double mutant in a synergistic fashion.
Redundant Mitochondrial Targeting Signals in Yeast Adenylate
Kinase*
,
*
This work was supported in part by Deutsche
Forschungsgemeinschaft Grant Ba415/24-1.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
Present address: Institut für Genetik und Allgemeine
Biologie, Universität Salzburg, Hellbrunnerstr. 34, A-5020
Salzburg, Austria.
§
To whom correspondence should be addressed. Tel.: 49-89-2180-6176;
Fax: 49-89-2180-6160; E-mail: W.Bandlow@lrz.uni-muenchen.de.
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