Mitochondrial DNA instability mutants of the bifunctional protein Ilv5p have altered organization in mitochondria and are targeted for degradation by Hsp78 and the Pim1p protease.
Ilv5p is a bifunctional mitochondrial protein in Saccharomyces cerevisiae required for branched-chain amino acid biosynthesis and for the stability of wild-type (rho(+)) mitochondrial DNA (mtDNA). Mutant forms of Ilv5p defective in mtDNA stability (a(+)D(-)) are present as 5-10 punctate structures in mitochondria, whereas mutants lacking enzymatic function (a(-)D(+)) show a reticular distribution, as does wild-type Ilv5p. a(+)D(-) ilv5 mutations are recessive, and the mutant protein is redistributed to a reticular form when co-expressed with wild-type Ilv5p. Ilv5p proteins that are punctate in vivo are also less soluble in detergent extracts of isolated mitochondria, suggesting that the punctate foci in a(+)D(-) Ilv5p mutants are aggregates of the protein. a(+)D(-) Ilv5p proteins are selectively degraded in cells lacking a functional mitochondrial genome, but only in cells grown under derepressing conditions. The targeted degradation of a(+)D(-) Ilv5p, which occurs even when co-expressed with wild-type Ilv5p, is mediated by the glucose-repressible chaperone, Hsp78, and by the ATP-dependent Pim1p protease, whose activity may be modulated by rho(+) mtDNA.
Bateman
Joseph M
JM
Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9148, USA.
Iacovino
Michelina
M
Perlman
Philip S
PS
Butow
Ronald A
RA
D049069:ATP-Dependent Proteases; D000429:Alcohol Oxidoreductases / Q000737:chemistry / Q000235:genetics*; D015153:Blotting, Western; D002455:Cell Division; D002845:Chromatography; D004272:DNA, Mitochondrial / Q000737:chemistry* / Q000235:genetics*; D005656:Fungal Proteins / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006360:Heat-Shock Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics*; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D012697:Serine Endopeptidases / Q000378:metabolism*; D013997:Time Factors
D004272:DNA, Mitochondrial; D005656:Fungal Proteins; C083349:HSP78 protein, S cerevisiae; D006360:Heat-Shock Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D000429:Alcohol Oxidoreductases; C470636:Ilv5 protein, S cerevisiae; D049069:ATP-Dependent Proteases; C085155:PIM1 protein, S cerevisiae; D012697:Serine Endopeptidases; D005947:Glucose