Cytosolic Reactions in Mitochondrial Protein Import
Cytosolic hsp70 molecules are involved in maintenance of pre-proteins in transport competent conformations. Genetic and biochemical studies in procaryotes indicate that hsp70 (DnaK) functionally interacts with two other cytosolic proteins, DnaJ and GrpE (Ang et al., 1991). Recently, several eukaryotic DnaJ homologs have been identified. We have purified cytosolic hsp70 (SSA1p) and DnaJ (YDJ1p) homologs from S. cerevisiae and characterized interactions between them. SSA1p exhibited a weak ATPase activity which was stimulated about 10 fold by YDJ1p. Stable complex formation between SSA1p and a mitochondria) presequence peptide was demonstrated. Significant reductions in complex formation were only observed in the presence of both ATP and YDJ1 p. Thus, an eukaryotic dnaJ homolog functionally interacts an eukaryotic hsp70 family member to regulate affinity of the chaperone for a polypeptide substrate.
KeywordsHeat Shock Transcription Factor Nascent Polypeptide Chain Hsp70 Homolog Cell BioI Mitochondrial Protein Import
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