Mitochondrial heat shock protein 70, a molecular chaperone for proteins encoded by mitochondrial DNA.
Mitochondrial heat shock protein 70 (mt-Hsp70) has been shown to play an important role in facilitating import into, as well as folding and assembly of nuclear-encoded proteins in the mitochondrial matrix. Here, we describe a role for mt-Hsp70 in chaperoning proteins encoded by mitochondrial DNA and synthesized within mitochondria. The availability of mt-Hsp70 function influences the pattern of proteins synthesized in mitochondria of yeast both in vivo and in vitro. In particular, we show that mt-Hsp70 acts in maintaining the var1 protein, the only mitochondrially encoded subunit of mitochondrial ribosomes, in an assembly competent state, especially under heat stress conditions. Furthermore, mt-Hsp70 helps to facilitate assembly of mitochondrially encoded subunits of the ATP synthase complex. By interacting with the ATP-ase 9 oligomer, mt-Hsp70 promotes assembly of ATP-ase 6, and thereby protects the latter protein from proteolytic degradation. Thus mt-Hsp70 by acting as a chaperone for proteins encoded by the mitochondrial DNA, has a critical role in the assembly of supra-molecular complexes.
Institut für Physiologische Chemie, Universität München, Germany.
J M
JM
Herrmann
R A
RA
Stuart
E A
EA
Craig
W
W
Neupert
D004272:DNA, Mitochondrial / Q000378:metabolism*; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000302:isolation & purification; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis* / Q000302:isolation & purification / Q000378:metabolism; D046911:Macromolecular Substances; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D006180:Proton-Translocating ATPases / Q000096:biosynthesis / Q000302:isolation & purification; D012270:Ribosomes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D013696:Temperature
D004272:DNA, Mitochondrial; D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D046911:Macromolecular Substances; D006180:Proton-Translocating ATPases