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  • 1
    Electronic Resource
    Electronic Resource
    The respiratory gene OXA1 has two fission yeast orthologues which together encode a function essential for cellular viability (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 35 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Saccharomyces cerevisiae nuclear gene OXA1, which is conserved from prokaryotes to human, was shown to be essential for cytochrome c oxidase and F1F0–ATP synthase biogenesis. We have searched for an orthologue of OXA1 in Schizosaccharomyces pombe, another yeast that is highly diverged from S. cerevisiae and which could more closely model higher eukaryotes. In particular, S. pombe exhibits a limited growth under anaerobic conditions and is petite negative, that is it does not tolerate large deletions of its mitochondrial DNA. Surprisingly, two S. pombe cDNAs able to complement an S. cerevisiae oxa1 mutation were isolated. The corresponding genes have different chromosomal locations and intron contents. They encode distinct proteins, both sharing a weak sequence identity one with the other and with Oxa1p. A phenotypic analysis of both single inactivations demonstrates that only one gene is essential for respiration in S. pombe. However, the double inactivation is lethal. This work gives new insight into the dependence of S. pombe viability upon oxa1 function, providing evidence of a connection between petite negativity, a functional respiratory chain and F1F0–ATP synthase complex in S. pombe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01781.x
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  • 2
    Electronic Resource
    Electronic Resource
    The NAM1/MTF2 nuclear gene product is selectively required for the stability and/or processing of mitochondrial transcripts of the atp6 and of the mosaic, cox1 and cytb genes in Saccharomyces cerevisiae (1993)
    Springer
    Molecular genetics and genomics 240 (1993), S. 419-427 
    Details
    ISSN: 1617-4623
    Keywords: Yeast ; Nucleo-mitochondrial intraction ; RNA processing ; RNA stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The NAM1/MTF2 gene was firstly isolated as a multicopy suppressor of mitochondrial splicing deficiencies and independently as a gene of which a thermosensitive allele affects mitochondrial transcription in organello. To determine which step in mitochondrial RNA metabolism is controlled in vivo by the NAM1 gene, mitochondrial transcripts of seven transcription units from strains carrying an inactive nam1::URA3 gene disruption in various mitochondrial genetic backgrounds were analysed by Northern blot hybridisations. In a strain carrying an intron-containing mitochondrial genome, the inactivation of the NAM1 gene led to a strong decrease in (or total absence of) the mosaic cytb and cox1 mRNAs and in transcripts of the atp6-rf3/ens2 genes, which are co-transcribed with cox1. Neither the accumulation of unspliced cytb or cox1 pre-mRNAs, nor that of excised circular intron molecules of ai1 or ai2 were observed, but the abundance of the bi1 and ai7 lariats was comparable to that observed in the wild-type strain, thus demonstrating that transcription of the cytb and cox1 genes does occur. In strains carrying the intron-less mitochondrial genome with or without the rf3/ens2 sequence, wild-type amounts of cytb and cox1 mRNAs were detected while the amount of the atp6 mRNA was always strongly decreased. The abundance of transcripts from five other genes was either slightly (21S rRNA) or not at all (cox2, cox3, atp9 and 15S rRNA) affected by the nam1 inactivation. This analysis leads to the conclusion that the NAM1 protein is not a general mitochondrial transcription factor, but rather is predominantly and selectively required for the processing and/or for the stability of cytb and cox1 intron-containing pre-mRNAs and of the atp6 transcripts. Since the original intronic mutations suppressed by the amplification of the NAM1 gene are situated in stem-loop rich structures, we propose that the NAM1 protein is a stem-loop RNA-binding protein that plays a role in determining RNA stability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280396
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  • 3
    Electronic Resource
    Electronic Resource
    Two adjacent nuclear genes, ISF1 and NAM7/UPF1, cooperatively participate in mitochondrial functions in Saccharomyces cerevisiae (1994)
    Springer
    Molecular genetics and genomics 242 (1994), S. 49-56 
    Details
    ISSN: 1617-4623
    Keywords: Nuclear suppressor gene ; Mitochondrial functions ; Glucose repression ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We previously isolated a nuclear 5.7 kb genomic fragment carrying the NAM7/UPF1 gene, which is able to suppress mitochondrial splicing deficiency when present in multiple copies. We show here that an immediately adjacent gene ISF1 (Increasing Suppression Factor) increases the efficiency of the NAM7/UPF1 suppressor activity. The ISF1 gene has been independently isolated as the MBR3 gene and comparison of the ISF1 predicted protein sequence with data libraries revealed a significant similarity with the MBRI yeast protein. The ISF1 and NAM7 genes are transcribed in the same direction, and RNase mapping allowed the precise location of their termini within the intergenic region to be determined. The ISF1 gene is not essential for cell viability or respiratory growth. However as for many mitochondrial genes, ISF1 expression is sensitive to fermentative repression; in contrast expression of the NAM7 gene is unaffected by glucose. We propose that ISF1 could influence the NAM7/UPF1 function, possibly at the level of mRNA turnover, thus modulating the expression of nuclear genes involved in mitochondrial biogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00277347
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  • 4
    Electronic Resource
    Electronic Resource
    Long range control circuits within mitochondria and between nucleus and mitochondria (1981)
    Springer
    Molecular genetics and genomics 184 (1981), S. 493-503 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the preceding paper of this series (Dujardin et al. 1980a) we described general methods of selecting and genetically characterizing suppressor mutations that restore the respiratory capacity of mit - mitochondrial mutations. Two dominant nuclear (NAM1-1 and NAM2-1) and one mitochondrial (mim2-1) suppressors are more extensively studied in this paper. We have analysed the action spectrum of these suppressors on 433 mit - mutations located in various mitochondrial genes and found that they preferentially alleviate the effects of mutations located within intron open reading frames of the cob-box gene. We conclude that these suppressors permit the maturation of cytochrome b mRNA by restoring the synthesis of intron encoded protein(s) catalytically involved in splicing i.e. mRNA-maturase(s) (cf. Lazowska et al. 1980). NAM1-1 is allele specific and gene non-specific: it suppresses mutations located within different introns. NAM2-1 and mim2-1 are intron-specific: they suppress mutations all located in the same (box7) intron of the cobbox gene. Analyses of cytochrome absorption spectra and mitochondrial translation products of cells in which the suppressors are associated with various other mit - mutations show that the suppressors restore cytochrome b and/or cytochrome oxidase (cox 1) synthesis, as expected from their growth phenotype. This suppression is, however, only partial: some new polypeptides characteristic of the mit - mutations can be still detected in the presence of suppressor. Interestingly enough when box7 specific suppressors NAM2-1 and mim2-1 are associated with a complete cob-box deletion (leading to a total deficiency of cytochrome b and oxidase) partial restoration of cox I synthesis is observed while cytochrome b is still totally absent. These results show that in strains carrying NAM2-1 or mim2-1 the presence of cytochrome b gene is no longer required for the expression of the oxi3 gene pointing out to the possibility of a mutational switch-on of silent genes, whether mitochondrial, mim2-1, or nuclear, NAM2-1. This switch-on would permit the synthesis of an active maturase acting as a substitute for the box7 maturase in order to splice the cytochrome b and oxidase mRNAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352529
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  • 5
    Electronic Resource
    Electronic Resource
    Novel class of nuclear genes involved in both mRNA splicing and protein synthesis in Saccharomyces cerevisiae mitochondria (1989)
    Springer
    Molecular genetics and genomics 215 (1989), S. 517-528 
    Details
    ISSN: 1617-4623
    Keywords: Yeast ; Nuclear genes ; Mitochondrial translation ; Mitochondrial splicing ; Suppression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have cloned three distinct nuclear genes, NAM1, NAM7, and NAM8, which alleviate mitochondrial intron mutations of the cytochrome b and COXI (subunit I of cytochrome oxidase) genes when present on multicopy plasmids. These nuclear genes show no sequence homology to each other and are localized on different chromosomes: NAM1 on chromosome IV, NAM7 on chromosome XIII and NAM8 on chromosome VIII. Sequence analysis of the NAM1 gene shows that it encodes a protein of 440 amino acids with a typical presequence that would target the protein to the mitochondrial matrix. Inactivation of the NAM1 gene by gene transplacement leads to a dramatic reduction of the overall synthesis of mitochondrial protein, and a complete absence of the COXI protein which is the result of a specific block in COXI pre-mRNA splicing. The possible mechanisms by which the NAM1 gene product may function are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00427051
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  • 6
    Electronic Resource
    Electronic Resource
    The cytochrome oxidase subunit I split gene in Saccharomyces cerevisiae: Genetic and physical studies of the mtDNA segment encompassing the ‘cytochrome b-homologous’ intron (1982)
    Springer
    Molecular genetics and genomics 188 (1982), S. 51-59 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have constructed a refined genetic and physical map of 38 oxi3 mutations. With the help of the rho - clones derived from ‘short’ and ‘long’ genes, pairwise crosses between mutants, estimations of their reversion frequencies and analyses of mitochondrially synthesized proteins, we have characterized and localized several mutants in the exon A4 and in the intron aI4. We present genetic and physical evidence that in the ‘long’ gene the exon A5 is split into at least three quite distinct exons, A5-1, A5-2 and A5-3 where numerous mutations are localized. We suggest that a novel 56 Kd polypeptide, which accumulates in some cis-dominant oxi3 - mutants results from the translation of the upstream exons and the downstream aI4 intron.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00332995
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  • 7
    Electronic Resource
    Electronic Resource
    Heat shock protein HSP60 can alleviate the phenotype of mitochondrial RNA-deficient temperature-sensitive mna2 pet mutants (1995)
    Springer
    Molecular genetics and genomics 246 (1995), S. 56-64 
    Details
    ISSN: 1617-4623
    Keywords: Temperature-sensitive mutants ; Heat shock protein 60 ; Conservative single amino acid substitutions ; Mitochondrial biogenesis ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract mna2, which belongs to the class I temperature-sensitive pet mutants that lose mitochondrial (mt)RNA at restrictive temperature, was shown by complementation and sequence determination to correspond to the gene coding for HSP60. Both mna2-1 and mna2-2, the two available alleles of mna2, have conservative single amino acid substitutions in the HSP60 gene. Valine substitutes for an alanine (position 47) in mna2-1, and an isoleucine substitutes for a valine (position 77) in mna2-2. These substitutions result in defects in respiration and in steady-state mtRNA accumulation. Wild-type hsp60 alleviates the mtRNA phenotype completely, while partially relieving the respiratory deficiency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00290133
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  • 8
    Electronic Resource
    Electronic Resource
    TheNAM8 gene inSaccharomyces cerevisiae encodes a protein with putative RNA binding motifs and acts as a suppressor of mitochondrial splicing deficiencies when overexpressed (1992)
    Springer
    Molecular genetics and genomics 233 (1992), S. 136-144 
    Details
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Nuclear gene ; Mitochondrial splicing ; Suppression ; RNA binding proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have characterized the nuclear geneNAM8 inSaccharomyces cerevisiae. It acts as a suppressor of mitochondrial splicing deficiencies when present on a multicopy plasmid. The suppressed mutations affect RNA folding and are located in both group I and group II introns. The gene is weakly transcribed in wildtype strains, its overexpression is a prerequisite for the suppressor action. Inactivation of theNAM8 gene does not affect cell viability, mitochondrial function or mitochondrial genome stability. TheNAM8 gene encodes a protein of 523 amino acids which includes two conserved (RNP) motifs common to RNA-binding proteins from widely different organisms. This homology with RNA-binding proteins, together with the intronic location of the suppressed mitochondrial mutations, suggests that the NAM8 protein could be a non-essential component of the mitochondrial splicing machinery and, when present in increased amounts, it could convert a deficient intron RNA folding pattern into a productive one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587571
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  • 9
    Electronic Resource
    Electronic Resource
    Large-scale phenotypic analysis - the pilot project on yeast chromosome III (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 13 (1997), S. 1547-1562 
    Details
    ISSN: 0749-503X
    Keywords: chromosome III ; drug-sensitivity/resistance ; functional analysis ; genome ; Saccharomyces cerevisiae ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In 1993, a pilot project for the functional analysis of newly discovered open reading frames, presumably coding for proteins, from yeast chromosome III was launched by the European Community. In the frame of this programme, we have developed a large-scale screening for the identification of gene/protein functions via systematic phenotypic analysis. To this end, some 80 haploid mutant yeast strains were constructed, each carrying a targeted deletion of a single gene obtained by HIS3 or TRP1 transplacement in the W303 background and a panel of some 100 growth conditions was established, ranging from growth substrates, stress to, predominantly, specific inhibitors and drugs acting on various cellular processes. Furthermore, co-segregation of the targeted deletion and the observed phenotype(s) in meiotic products has been verified. The experimental procedure, using microtiter plates for phenotypic analysis of yeast mutants, can be applied on a large scale, either on solid or in liquid media. Since the minimal working unit of one 96-well microtiter plate allows the simultaneous analysis of at least 60 mutant strains, hundreds of strains can be handled in parallel. The high number of monotropic and pleiotropic phenotypes (62%) obtained, together with the acquired practical experience, have shown this approach to be simple, inexpensive and reproducible. It provides a useful tool for the yeast community for the systematic search of biochemical and physiological functions of unknown genes accounting for about a half of the 6000 genes of the complete yeast genome. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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