YGE1p, a Eukaryotic GRP-E Homolog, Is Localized in the Mitochondrial Matrix and Interacts with Mitochondrial HSP70

Yeast Yge1p, the gene product of YGE1, is a eukaryotic GrpE homolog found recently (Ikeda et al., 1994). We have revealed here that Yge1p is a soluble protein in the mitochondrial matrix. Depletion of Yge1p in yeast cells resulted in accumulation of the precursor of F1-ATPase β subunit in vivo, suggesting that Yge1p is involved in protein import into mitochondria. Overexpression of Yge1p in the temperature-sensitive mutant strains of mitochondrial hsp70, Ssc1p, caused hypersensitivity to temperature for cell growth, suggesting a genetic interaction between the YGE1and SSC1genes. A physical interaction between Yge1p and Ssc1p was directly demonstrated by co-immunoprecipitation of Ssc1p by the anti-Yge1p antibodies. We propose that Yge1p functions in cooperation with Ssc1p in a similar manner as bacterial GrpE with DnaK.