The cold sensitivity of a mutant of Saccharomyces cerevisiae lacking a mitochondrial heat shock protein 70 is suppressed by loss of mitochondrial DNA.
SSH1, a newly identified member of the heat shock protein (hsp70) multigene family of the budding yeast Saccharomyces cerevisiae, encodes a protein localized to the mitochondrial matrix. Deletion of the SSH1 gene results in extremely slow growth at 23 degrees C or 30 degrees C, but nearly wild-type growth at 37 degrees C. The matrix of the mitochondria contains another hsp70, Ssc1, which is essential for growth and required for translocation of proteins into mitochondria. Unlike SSC1 mutants, an SSH1 mutant showed no detectable defects in import of several proteins from the cytosol to the matrix compared to wild type. Increased expression of Ssc1 partially suppressed the cold-sensitive growth defect of the SSH1 mutant, suggesting that when present in increased amounts, Ssc1 can at least partially carry out the normal functions of Ssh1. Spontaneous suppressors of the cold-sensitive phenotype of an SSH1 null mutant were obtained at a high frequency at 23 degrees C, and were all found to be respiration deficient. 15 of 16 suppressors that were analyzed lacked mitochondrial DNA, while the 16th had reduced amounts. We suggest that Ssh1 is required for normal mitochondrial DNA replication, and that disruption of this process in ssh1 cells results in a defect in mitochondrial function at low temperatures.
Schilke
B
B
Department of Biomolecular Chemistry, University of Wisconsin, Madison 53706, USA.
Forster
J
J
Davis
J
J
James
P
P
Walter
W
W
Laloraya
S
S
Johnson
J
J
Miao
B
B
Craig
E
E
D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D003080:Cold Temperature; D004271:DNA, Fungal / Q000502:physiology; D004272:DNA, Mitochondrial / Q000502:physiology; D005656:Fungal Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005800:Genes, Fungal / Q000235:genetics; D018840:HSP70 Heat-Shock Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008928:Mitochondria / Q000737:chemistry / Q000378:metabolism*; D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D011498:Protein Precursors / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins; D013489:Suppression, Genetic
D004271:DNA, Fungal; D004272:DNA, Mitochondrial; D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; C115913:SSQ1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins