Mdj1p, a novel chaperone of the DnaJ family, is involved in mitochondrial biogenesis and protein folding

Mdj1p, a novel member of the DnaJ family, is a heat shock protein
that is associated with the inner membrane of mitochondria of
Saccharomyces cerevisiae. Disruption of the MDJ1 gene resulted in a
petite phenotype, loss of mitochondrial DNA, and inviability at
37°C. Import of precursor proteins was not affected by a lack of
Mdj1p, but folding of newly imported proteins was markedly
impaired. The efficiency of refolding of a tester protein,
dihydrofolate reductase, was significantly reduced in mitochondria
lacking Mdj1p after incubation at elevated temperature. We conclude
that Mdj1p is an important mitochondrial chaperone that
participates in the folding of newly imported proteins and in the
protection of proteins against heat denaturation and aggregation.