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© The Rockefeller University Press, 0021-9525/1997//1089 $5.00
The Journal of Cell Biology, Volume 139, Number 5, , 1997 1089-1095

Article

The Human DnaJ Homologue dj2 Facilitates Mitochondrial Protein Import and Luciferase Refolding



Kazutoyo Terada*, Masaki Kanazawa*, Bernd Bukau{ddagger}, and Masataka Mori*

* Department of Molecular Genetics, Kumamoto University School of Medicine, Kumamoto 862, Japan; and {ddagger} Institut für Biochemie und Molekularbiologie, D-79104 Freiburg, Germany

DnaJ homologues function in cooperation with hsp70 family members in various cellular processes including intracellular protein trafficking and folding. Three human DnaJ homologues present in the cytosol have been identified: dj1 (hsp40/hdj-1), dj2 (HSDJ/hdj-2), and neuronal tissue-specific hsj1. dj1 is thought to be engaged in folding of nascent polypeptides, whereas functions of the other DnaJ homologues remain to be elucidated. To investigate roles of dj2 and dj1, we developed a system of chaperone depletion from and readdition to rabbit reticulocyte lysates. Using this system, we found that heat shock cognate 70 protein (hsc70) and dj2, but not dj1, are involved in mitochondrial import of preornithine transcarbamylase. Bacterial DnaJ could replace mammalian dj2 in mitochondrial protein import. We also tested the effects of these DnaJ homologues on folding of guanidine-denatured firefly luciferase. Unexpectedly, dj2, but not dj1, together with hsc70 refolded the protein efficiently. We propose that dj2 is the functional partner DnaJ homologue of hsc70 in the mammalian cytosol. Bacterial DnaJ protein could replace mammalian dj2 in the refolding of luciferase. Thus, the cytosolic chaperone system for mitochondrial protein import and for protein folding is highly conserved, involving DnaK and DnaJ in bacteria, Ssa1–4p and Ydj1p in yeast, and hsc70 and dj2 in mammals.

1. Abbreviations used in this paper: dj1, mammalian counterpart of hsp40/ hdj-1; dj2, mammalian counterpart of HSDJ/hdj-2; His-dj1 and His-dj2, hexahistidine-tagged dj1 or dj2; hsc70, 70K heat shock cognate protein; pOTC, preornithine transcarbamylase.

Please address all correspondence to M. Mori, Department of Molecular Genetics, Kumamoto University School of Medicine, Kuhonji 4-24-1, Kumamoto 862, Japan. Tel.: (81) 96-373-5140. Fax: (81) 96-373-5145. e-mail: masa{at}gpo.kumamoto-u.ac.jp

The current address of M. Kanazawa is Department of Pediatrics, Chiba University School of Medicine, Chiba 280, Japan.


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