hide
Free keywords:
Amino Acid Sequence
Biological Transport
Calcium-Binding Proteins/metabolism
Carrier Proteins/metabolism
Cloning, Molecular
Fungal Proteins/genetics/*metabolism
HSP70 Heat-Shock Proteins/*metabolism
Heat-Shock Proteins/genetics/*metabolism
Membrane Proteins/metabolism
Mitochondria/*metabolism
*Mitochondrial Membrane Transport Proteins
Molecular Sequence Data
Mutation
Peptides/metabolism
Protein Folding
Saccharomyces cerevisiae/genetics/*metabolism
*Saccharomyces cerevisiae Proteins
Temperature
Abstract:
Hsp78 is a Clp homologue within mitochondria of Saccharomyces cerevisiae. Deletion of HSP78 does not cause any detectable changes in wild type cells, but results in a petite phenotype in the ssc1-3 mutant strain carrying a temperature-sensitive allele of mt-hsp70. When overexpressed in the ssc1-3 mutant strain, hsp78 suppresses the defect in mitochondrial protein import under permissive conditions in vitro and interacts directly with newly imported polypeptide chains. As a molecular chaperone, hsp78 prevents the aggregation of misfolded proteins in the matrix of mitochondria under conditions of impaired mt-hsp70 function. However, unlike misfolded proteins associated with mt-hsp70, hsp78-bound polypeptides are not efficiently degraded by the ATP-dependent PIM1 protease. Thus, hsp78 can partially substitute for mt-hsp70 functions in the assembly of mitochondria and may be part of a salvage pathway if mt-hsp70 is limiting.
