Mitochondrial protein import: isolation and characterization of the Saccharomyces cerevisiae MFT1 gene

Abstract

Mitochondrial targeting of an Atp2-LacZ fusion protein confers a respiration-defective phenotype on yeast cells. This effect has been utilized to select strains that grow on nonfermentable carbon sources, some of which have decreased levels of hybrid protein localized to the organelle. Many of the mutants obtained were also temperature-sensitive for growth on all media. The recessive mft (mitochondrial fusion targeting) mutants have been assigned to three complementation groups. MFT1 was cloned and sequenced: it encodes a 255 amino acid protein that is highly basic and has no predicted membrane-spanning domains or organelle-targeting sequences. The MFT1 gene is 91% identical to an open reading frame 3' of the SIR3 gene. Evidence is presented that these two closely related genes could represent a recent gene duplication.

Analysis of genes encoding highly conserved lysine‐rich proteins in Aplysia californica and Saccharomyces cerevisiae

“…Interestingly, the HSE, which is usually found 15-18 bp upstream of the TATA box (Bienz, 1985), is found 17 bp upstream of the sequence ATAATATA, in KRP-Yl. The presence of a potential HSE in the promoter of KRP-YI gene is consistent with the fact that the transcript steady-state concentrations of the two genes are quite different; that of MFTl (KRP-Y2) is high, that of KRP-YI mRNA is barely detectable (Garrett et al, 1991). This could indicate that one gene (KRP-Y2) is always expressed, as seen in Aplysia, rat and mouse, while the other (KRP-YI) is inducible.…”

“…V..C.....GSEDHS...I..RVD....K.L....H..DF.T...R...R.... 0 ................... A ....... T.D...K.C....H..D.....M......... G ................... A ....... T.D...K.C....H..D.. ... M ......... 0 ................... A.......T.D...K.C....H..D Garrett et al, 1991), rat FTE-1 (Kho and Zarbl, 1992), human hRPS3a (Metspalu et al, 1992), mouse MUSTUMSEQA (Gordon et al, 1992) and higher plant CYCO7 (It0 et al, 1991). In comparison to the KRP-A sequence, dots and dashes represent identical and addeddeleted amino acids, respectively.…”

“…In yeast, the MFTI gene has been identified as coding for a protein involved in protein import into mitochondria (Garrett et al, 1991). The authors suggest that the MFTl protein is needed for folding/antifolding of proteins prior to import into mitochondria.…”

“…Mutation of the gene impairs the transport of a fusion protein into mitochondria. Disruption of the gene indicates that it is not essential for growth at 30"C, although the cells grow more slowly (Garrett et al, 1991). However, its disruption is lethal at 37°C.…”

“…It is more difficult to explain why the disruption is lethal at 37"C, since the normal expression of the KRP-Y genes is repressed at this temperature. It is possible that the disruption of the gene located downstream of MFTI, which was also partly deleted by the disruption protocol used by Garrett et al (1991) is responsible for the ts phenotype at 37°C.…”