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Department of Cell Biology and Anatomy, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
We have identified a new protein, Tim54p,
located in the yeast mitochondrial inner membrane.
Tim54p is an essential import component, required for
the insertion of at least two polytopic proteins into the
inner membrane, but not for the translocation of precursors into the matrix. Several observations suggest
that Tim54p and Tim22p are part of a protein complex
in the inner membrane distinct from the previously
characterized Tim23p-Tim17p complex. First, multiple
copies of the TIM22 gene, but not TIM23 or TIM17, suppress the growth defect of a tim54-1 temperature-sensitive mutant. Second, Tim22p can be coprecipitated
with Tim54p from detergent-solubilized mitochondria,
but Tim54p and Tim22p do not interact with either
Tim23p or Tim17p. Finally, the tim54-1 mutation destabilizes the Tim22 protein, but not Tim23p or Tim17p.
Our results support the idea that the mitochondrial inner membrane carries two independent import complexes: one required for the translocation of proteins
across the inner membrane (Tim23p-Tim17p), and the
other required for the insertion of proteins into the inner membrane (Tim54p-Tim22p).
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