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.