The DNA helicase, Hmi1p, is transported into mitochondria by a C-terminal cleavable targeting signal.
We have identified a novel mitochondrial targeting signal in the precursor of the DNA helicase Hmi1p of Saccharomyces cerevisiae that is located at the C terminus of the protein. Similar to classical N-terminal presequences, this C-terminal targeting signal consists of a stretch of positively charged amino acids that has the potential to form an amphipathic alpha-helix. Deletion of the C-terminal 36 amino acids of helicase resulted in loss of import into mitochondria, while deletion of the N-terminal 40 amino acids had no effect. When C-terminal regions of the helicase were placed at the C terminus of a passenger protein, dihydrofolate reductase, the resulting fusion proteins were directed into the mitochondrial matrix, and the C-terminal region of helicase became proteolytically processed. Import of helicase occurs in a C- to N-terminal direction; it requires a membrane potential and the TIM17-23 translocase together with mitochondrial Hsp70. Helicase is the only mitochondrial matrix protein identified thus far with a cleavable targeting signal at its C terminus.
Institut für Physiologische Chemie der Universität München, Goethestrasse 33, 80336 München, Germany.
C M
CM
Lee
J
J
Sedman
W
W
Neupert
R A
RA
Stuart
D000595:Amino Acid Sequence; D001692:Biological Transport; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D012441:Saccharomyces cerevisiae / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins
D005656:Fungal Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D004265:DNA Helicases; C120692:HMI1 protein, S cerevisiae