Requirement of different mitochondrial targeting sequences of the yeast mitochondrial transcription factor Mtf1p when synthesized in alternative translation systems.
Mitochondrial (mt) translocation of the nuclearly encoded mt transcription factor Mtf1p appears to occur independent of a cleavable presequence, mt receptor, mt membrane potential or ATP [Biswas and Getz (2002) J. Biol. Chem. 277, 45704-45714]. To understand further the import strategy of Mtf1p, we investigated the import of the wild-type and N-terminal-truncated Mtf1p mutants synthesized in two different in vitro translation systems. These Mtf1p derivatives were generated either in the RRL (rabbit reticulocyte lysate) or in the WGE (wheat germ extract) translation system. Under the in vitro import conditions, the RRL-synthesized full-length Mtf1p but not the N-terminal-truncated Mtf1p product was efficiently imported into mitochondria, suggesting that the N-terminal sequence is important for its import. On the other hand, when these Mtf1p products were generated in the WGE system, surprisingly, the N-terminal-truncated products, but not the full-length protein, were effectively translocated into mitochondria. Despite these differences between the translation systems, in both cases, import occurs at a low temperature and has no requirement for a trypsin-sensitive mt receptor, mt membrane potential or ATP hydrolysis. Together, these observations suggest that, in the presence of certain cytoplasmic factors (derived from either RRL or WGE), Mtf1p is capable of using alternative import signals present in different regions of the protein. This appears to be the first example of usage of different targeting sequences for the transport of a single mt protein into the mt matrix.
Biswas
Tapan K
TK
Department of Pathology, University of Chicago, 5841 South Maryland Avenue, Chicago, IL 60637, USA. tbiswas@midway.uchicago.edu
Getz
Godfrey S
GS
D000818:Animals; D002412:Cations / Q000378:metabolism / Q000494:pharmacology; D002474:Cell-Free System; D002614:Chelating Agents / Q000494:pharmacology; D004317:Doxorubicin / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials; D008670:Metals / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D010743:Phospholipids / Q000378:metabolism; D010936:Plant Extracts / Q000737:chemistry; D021382:Protein Sorting Signals / Q000235:genetics / Q000502:physiology*; D021381:Protein Transport / Q000187:drug effects; D011817:Rabbits; D019163:Reducing Agents / Q000378:metabolism / Q000494:pharmacology; D012156:Reticulocytes / Q000737:chemistry; D012260:Ribonucleases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion / Q000235:genetics; D013438:Sulfhydryl Compounds / Q000378:metabolism / Q000494:pharmacology; D013696:Temperature; D014157:Transcription Factors / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014178:Translocation, Genetic / Q000502:physiology*; D014908:Triticum; D014357:Trypsin / Q000378:metabolism
D002412:Cations; D002614:Chelating Agents; C071720:MTF1 protein, S cerevisiae; D008670:Metals; D024101:Mitochondrial Proteins; D010743:Phospholipids; D010936:Plant Extracts; D021382:Protein Sorting Signals; D019163:Reducing Agents; D029701:Saccharomyces cerevisiae Proteins; D013438:Sulfhydryl Compounds; D014157:Transcription Factors; D004317:Doxorubicin; D012260:Ribonucleases; D014357:Trypsin