PMID:1978929

Citation	Cheng, MY, Hartl, FU and Horwich, AL (1990) The mitochondrial chaperonin hsp60 is required for its own assembly. Nature 348:455-8
Abstract	Heatshock protein 60 (hsp60) in the matrix of mitochondria is essential for the folding and assembly of newly imported proteins. Hsp60 belongs to a class of structurally related chaperonins found in organelles of endosymbiotic origin and in the bacterial cytosol. Hsp60 monomers form a complex arranged as two stacked 7-mer rings. This 14-mer complex binds unfolded proteins at its surface, then seems to catalyse their folding in an ATP-dependent process. The question arises as to how such an assembly machinery is itself folded and assembled. Hsp60 subunits are encoded by a nuclear gene and translated in the cytosol as precursors which are translocated into mitochondria and proteolytically processed. In both intact cells and isolated mitochondria of the hsp60-defective yeast mutant mif4, self-assembly of newly imported wild-type subunits is not observed. Functional pre-existing hsp60 complex is required in order to form new, assembled, 14-mer. Subunits imported in vitro are assembled with a surprisingly fast half-time of 5-10 min, indicative of a catalysed reaction. These findings are further evidence that self-assembly may not be the principal mechanism by which proteins attain their functional conformation in the intact cell.
Links	PubMed Online version:10.1038/348455a0
Keywords	Biological Transport; Chaperonin 60; Chaperonins; Electrophoresis, Polyacrylamide Gel; Fungal Proteins/metabolism; Heat-Shock Proteins/physiology; Macromolecular Substances; Mitochondria/metabolism; Molecular Weight; Protein Conformation; Protein Precursors/metabolism; Proteins/physiology; Saccharomyces cerevisiae
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