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  • 1
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Mitochondrial trp-tRNA synthetase ; Nuclear mutation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The conditional respiratory-deficient Saccharomyces cerevisiae mutant pet-ts2281 was complemented by an yeast genomic DNA library. The gene thus isolated was sequenced and proved to be identical to the known MSW1 sequence encoding mitochondrial tryptophanyl-tRNA synthetase (Myers and Tzagoloff 1985). Compared to the wild-type, the ts2281 mutant allele of MSW1 contained a single T→C transition leading to a Leu→Ser replacement at position 294 of the protein sequence. In addition to this mutational alteration, our sequence data for the wild-type gene differ from the originally published MSW1 sequence at five other DNA positions which affect two locally restricted regions of the polypeptide chain. As expected, at the non-permissive temperature ts2281 cells are specifically defective in mitochondrial trp-tRNA formation and, thus, in overall mitochondrial protein synthesis. In addition, the patterns of cytochrome b mRNA maturation intermediates were distinctly different in ts2281 and wild-type yeast cells. The mutational effect of the observed amino-acid substitution in ts2281 is discussed in terms of weakened hydrogen bonding in the C-terminal half of the MSW1-encoded protein.
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  • 2
    ISSN: 1432-0983
    Keywords: Mitochondria ; Ribosomal protein ; Nuclear gene ; pet mutant ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Saccharomyces cerevisiae nuclear gene MRP-L6 was cloned by complementation of the respiratory-deficient mutant pet-ts 2523 with a library of wildtype yeast genomic DNA. The isolated gene was part of a 3.8-kb sequenced DNA fragment containing, in addition to MRP-L6, two unassigned reading frames, ORF1 and ORF2. MRP-L6 codes for a basic protein of 205 amino acids and a molecular mass of 22.8 kDa. The protein exhibits significant sequence similarity to the ribosomal protein L6 of bacteria and chloroplasts. Unlike the corresponding bacterial proteins, however, the MRP-L6 protein (MRP-L6p) contains at its N-terminus a 16 amino-acid leader sequence exhibiting the known characteristics of mitochondrial import signals. Disruption of MRP-L6 leads to the phenotype of a mitochondrial translation-defective, rho-negative yeast mutant. The results are consistent with MRP-L6p representing an essential component of yeast mitochondrial ribosomes. Expression of MRP-L6 was examined, under conditions of glucose repression and derepression, in wild-type cells and in a series of catabolite repression-defective yeast mutants. In most cases, a distinct though small influence of the carbon source on the expression of an MRP-L6/lacZ reporter construct was observed.
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  • 3
    ISSN: 1432-0983
    Keywords: Mitochondrial import ; Precursor processing ; Yeast nuclear genes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Several nuclear mutants of the yeast, Saccharomyces cerevisiae, have been characterized which synthesize only the higher-molecular weight precursor but not the mature subunit VI of the mitochondrial ubiquinol cytochrome c oxidoreductase. The mutants belong to different complementation groups and vary in the extent of their being simultaneously deficient in other components of the mitochondrial inner membrane. From a yeast genomic DNA library the plasmid pTS2326 was isolated which complements the defect in one of these mutants, ts2326. The cloned DNA fragment, 2.3 kilobases in length, was sequenced. It contains two open reading frames, ORF1 and ORF2, consisting of 723 and 417 base pairs, respectively. By selective deletion of either reading frame it was shown that only ORF1 containes the information necessary to complement the ts2326 mutation. The ORF1 coding sequence is not the structural gene of subunit VI. The postulated gene product of ORF1 has a molecular weight of 27.114 daltons. It exhibits several sequence characteristics typical of proteins which are internalized by the mitochondrial membrane systems. It is proposed that ORF1 is involved in the import and processing of cytoplasmically synthesized mitochondrial precursors.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 64 (1977), S. 366-370 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Notes: Abstract Genetic as well as biochemical data suggest that the yeast fatty-acid synthetase complex has an (AB)6 protein structure where A and B represent multifunctional polypeptide chains with molecular weights of 185000 and 180000 daltons, respectively. Subunit A contains at least 3 and subunit B4 of the 8 known biochemical functions of the multienzyme complex. It is concluded that this complex structure has evolved from the corresponding prokaryotic system of monofunctional enzymes due to a selective advantage regarding the biosynthesis and assembly of the complex components.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 83 (1996), S. 347-358 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 83 (1996), S. 347-358 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
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  • 7
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Using two different experimental approaches—UV induced mitotic recombination and meiotic segregation—a fatty acid synthetase gene locus has been mapped on chromosome Fragment V of the Saccharomyces cerevisiae genetic map. This locus has been tentatively designated as fas1AB since it is a complex locus coding for at least two different fatty acid synthetase component enzymes, namely the β-hydroxyacid dehydratase and the enoyl reductase. According to the meiotic segregation patterns obtained, fas1AB is 41.6 centimorgans from ura1 and 35.7 centimorgans from trp3. Furthermore, the same criteria of mitotic sectoring and meiotic segregation indicate that the second known fatty acid synthetase gene cluster in yeast is genetically unlinked to fas1AB or to any other of the known genetic loci on Fragment V.
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  • 8
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Of 43 non-complementing alleles studied of the Saccharomyces cerevisiae fatty acid synthetase locus fas 1, 27 are reverted by external suppressors whereas 16 are susceptible only to intragenic suppression. Of the externally suppressible mutants 12 are reverted by both, amber and ochre suppressors, another 12 only by amber suppressors, and 3 are not suppressed by either of them. According to their response to the acridine mustard, ICR-191, one of the mutants not suppressible by external suppressors appears to be a frameshift mutation, whereas the others are suggested to be missense mutations. By X-ray induced mitotic recombination a genetic fine structure map of the complementing as well as of the noncomplementing fas 1-alleles was constructed. It was found that the alleles of the non-pleiotropic complementation groups II, Va, Vb and Vc map at distinct and characteristic regions within fas 1, each of them covering 9.8, 13.5, 5.3 and 1.6 X-ray map units, respectively. On the other hand, the non-complementing fas 1-alleles are distributed randomly over the entire locus, no matter whether they were nonsense or missense mutations. These non-complementing alleles are spread over a DNA region of 72 X-ray map units length and all the complementing alleles studied map within this region. These results suggest that fas 1 encodes only one, functionally complex, polypeptide chain.
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  • 9
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary From a Saccharomyces cerevisiae gene bank contained in the novel yeast cosmid shuttle vector pMS201 the fatty acid synthetase (FAS) genes FAS1 and FAS2 were isolated. FAS clones were identified by in situ colony hybridization using two yeast DNA probes apparently capable of producing avian FAS cross-reacting material (J. Carbon, personal communication). Classification as FAS1 or FAS2 clones was achieved by their specific transformation of fas1 and fas2 yeast mutants. By transcription mapping FAS1 was assigned to about 5.3 kb within 14.8 kb of chromosomal DNA covered by two genomically adjacent BamHI fragments. The FAS2 gene was localized on a single BamHI fragment of 25 kb. One of the FAS clones (FAS2) produces immunologically cross-reacting material in Escherichia coli. High frequency transformation of fas1 mutants was only observed with one subclone, pMS3021, containing the intact FAS1 locus. Other DNA segments cloned in the same self-replicating vector but representing only part of FAS1 exhibited drastically lower transformation rates. As evident from this and from FAS1/TRP1-contransformation rates only the intact FAS1 gene in pMS3021 is capable of fas1-mutant complementation. With partial FAS1 genes, even when coding for an intact equivalent of the mutated domain, their chromosomal integration is necessary for the expression of FAS. In intergrative transformants the coexistence of integrated and autonomously replicating plasmid DNA was demonstrated. Both, the extrachromosomal and chromosomally integrated FAS DNA was mitotically unstable. Transformation studies using subcloned FAS1 DNA segments revealed the relative locations of the enoyl reductase and dehydratase domains within this pentafunctional cluster gene.
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  • 10
    ISSN: 1617-4623
    Keywords: Yeast fatty acid synthetases ; Yarrowia lipolytica/Saccharomyces cerevisiae FAS1 sequence comparison ; S. cerevisiae FAS1 sequence correction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The fatty acid synthetase (FAS) gene FAS1 of the alkane-utilizing yeast Yarrowia lipolytica was cloned and sequenced. The gene is represented by an intron-free reading frame of 6228 by encoding a protein of 2076 amino acids and 229980 Da molecular weight. This protein exhibits a 58% sequence similarity to the corresponding Saccharomyces cerevisiae FAS β-subunit. The sequential order of the five FAS1-encoded enzyme domains, acetyl transferase, enoyl reductase, dehydratase and malonyl/palmityl-transferase, is co-linear in both organisms. This finding agrees with available evidence that the functional organization of FAS genes is similar in related organisms but differs considerably between unrelated species. In addition, previously reported conflicting data concerning the 3′ end of S. cerevisiae FAS1 were re-examined by genomic and cDNA sequencing of the relevant portion of the gene. Thereby, the translational stop codon was shown to lie considerably downstream of both published termination sites. The S. cerevisiae FAS1 gene thus has a corrected length of 6153 by and encodes a protein of 2051 amino acids and 228667 Da molecular weight.
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