Preproteins of chloroplast envelope inner membrane contain targeting information for receptor-dependent import into fungal mitochondria.
The amino-terminal transit sequences of two preproteins destined for the chloroplast inner envelope membrane show similarities to mitochondrial presequences in the prevalence of positive charges and the potential formation of an amphipathic alpha-helix. We studied if these preproteins could be imported into mitochondria and found a low, yet significant import into isolated plant mitochondria. The plant mitochondria were previously shown not to import precursors of chloroplast stromal or thylakoidal proteins. To analyze the specificity of import into mitochondria we used the established import systems of fungal mitochondria. The envelope preproteins were efficiently imported into Saccharomyces cerevisiae or Neurospora crassa mitochondria. Their import showed the characteristics of specific mitochondrial protein uptake, including a requirement for the main receptor MOM19 (mitochondrial outer membrane protein of 19 kDa) and a membrane potential across the inner membrane, and depended on the presence of the chloroplast transit sequence. We conclude that some chloroplast transit sequences contain sufficient information for specific interaction with mitochondrial import receptors (at least from fungal sources).
Brink
S
S
Julius-von Sachs-Institut für Biowissenschaften, Universität Würzburg, Federal Republic of Germany.
Flügge
U I
UI
Chaumont
F
F
Boutry
M
M
Emmermann
M
M
Schmitz
U
U
Becker
K
K
Pfanner
N
N
D001203:Ascomycota / Q000378:metabolism*; D001692:Biological Transport; D002451:Cell Compartmentation; D002736:Chloroplasts / Q000502:physiology*; D007425:Intracellular Membranes / Q000737:chemistry; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D009492:Neurospora crassa / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013045:Species Specificity
D033681:Mitochondrial Membrane Transport Proteins; D010940:Plant Proteins; D011498:Protein Precursors; D018160:Receptors, Cytoplasmic and Nuclear; D029701:Saccharomyces cerevisiae Proteins; C489350:TOM20 protein, S cerevisiae