Targeting of a chemically pure preprotein to mitochondria does not require the addition of a cytosolic signal recognition factor.
To analyze the role of cytosolic cofactors in mitochondrial protein targeting, we prepared a chemically pure mitochondrial preprotein. When diluted out of 7 M urea, this precursor protein was efficiently imported into mitochondria without the addition of cytosolic cofactors. Extensive prewashing of mitochondria (up to 2 M KCl) did not reduce its import. Import of the purified precursor showed the characteristics of authentic mitochondrial import including use of the receptor MOM19, requirement for a membrane potential, and proteolytic processing. When the precursor was preincubated at a low concentration of urea, cytosolic cofactors were needed to preserve its import competence. We conclude that targeting of this preprotein via the mitochondrial master receptor MOM19 does not require a cytosolic signal recognition factor; cytosolic cofactors apparently have chaperone-like functions in mitochondrial protein uptake. Moreover, we found that a cleavable presequence was sufficient to direct protein import via MOM19. Together with the cofactor-independent function of MOM19, it is thus conceivable that MOM19 functions as mitochondrial presequence receptor.
Becker
K
K
Institut für Physiologische Chemie, Universität München, Federal Republic of Germany.
Guiard
B
B
Rassow
J
J
Söllner
T
T
Pfanner
N
N
D000818:Animals; D002872:Chromosome Deletion; D004926:Escherichia coli / Q000235:genetics; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D042844:L-Lactate Dehydrogenase (Cytochrome); D008928:Mitochondria / Q000378:metabolism*; D009492:Neurospora crassa / Q000201:enzymology / Q000235:genetics; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000235:genetics / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012156:Reticulocytes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*
D011498:Protein Precursors; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D007770:L-Lactate Dehydrogenase; D042844:L-Lactate Dehydrogenase (Cytochrome); D006180:Proton-Translocating ATPases