Suppression of a defect in mitochondrial protein import identifies cytosolic proteins required for viability of yeast cells lacking mitochondrial DNA.
The TIM22 complex, required for the insertion of imported polytopic proteins into the mitochondrial inner membrane, contains the nonessential Tim18p subunit. To learn more about the function of Tim18p, we screened for high-copy suppressors of the inability of tim18Delta mutants to live without mitochondrial DNA (mtDNA). We identified several genes encoding cytosolic proteins, including CCT6, SSB1, ICY1, TIP41, and PBP1, which, when overproduced, rescue the mtDNA dependence of tim18Delta cells. Furthermore, these same plasmids rescue the petite-negative phenotype of cells lacking other components of the mitochondrial protein import machinery. Strikingly, disruption of the genes identified by the different suppressors produces cells that are unable to grow without mtDNA. We speculate that loss of mtDNA leads to a lowered inner membrane potential, and subtle changes in import efficiency can no longer be tolerated. Our results suggest that increased amounts of Cct6p, Ssb1p, Icy1p, Tip41p, and Pbp1p help overcome the problems resulting from a defect in protein import.
D017920:Antiporters / Q000235:genetics* / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004272:DNA, Mitochondrial; D018628:Gene Dosage; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D009154:Mutation; D021381:Protein Transport / Q000235:genetics / Q000502:physiology; D011506:Proteins / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism
D017920:Antiporters; C088425:CCT6 protein, S cerevisiae; D002352:Carrier Proteins; D004272:DNA, Mitochondrial; D018840:HSP70 Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; C116076:PBP1 protein, S cerevisiae; D011506:Proteins; C095192:SSB1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C102549:TIM22 protein, S cerevisiae; C444301:TIP41 protein, S cerevisiae; C403803:Tim18 protein, S cerevisiae; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins; D006180:Proton-Translocating ATPases; C471230:ATP2 protein, S cerevisiae