A new type of frameshift mutation in a mitochondrial genome

Poster (1998, June)

Biochemical, genetic and molecular characterization of respiratory-deficient mutants in the unicellular green alga Chlamydomonas reinhardtii

Poster (1996, August)

Transcription de gènes d'ARN de transfert dans les mitochondries de plantes supérieures

Scientific conference (1996)

A single editing event is a prerequisite for efficient processing of potato mitochondrial phenylalanine tRNA

in Molecular & Cellular Biology (1996), 16(7), 3504-3510

In bean, potato, and Oenothera plants, the C encoded at position 4 (C-4) in the mitochondrial tRNA(GAA)(Phe) gene is converted into a U in the mature tRNA, This nucleotide change corrects a mismatched C-4 ... [more ▼]

In bean, potato, and Oenothera plants, the C encoded at position 4 (C-4) in the mitochondrial tRNA(GAA)(Phe) gene is converted into a U in the mature tRNA, This nucleotide change corrects a mismatched C-4-A(69) base pair which appears when the gene sequence is folded into the cloverleaf structure. C-to-U conversions constitute the most common editing events occurring in plant mitochondrial mRNAs. While most of these conversions introduce changes in the amino acids specified by the mRNA and appear to be essential for the synthesis of functional proteins in plant mitochondria, the putative role of mitochondrial tRNA editing has not yet been defined. Since the edited form of the tRNA has the correct secondary and tertiary structures compared with the nonedited form, the two main processes which might be affected by a nucleotide conversion are aminoacylation and maturation. To test these possibilities, we determined the aminoacylation properties of unedited and edited potato mitochondrial tRNA(Phe) in vitro transcripts, as well as the processing efficiency of in vitro-synthesized potato mitochondrial tRNA(Phe) precursors. Reverse transcription-PCR amplification of natural precursors followed by cDNA sequencing was also used to investigate the influence of editing on processing. Our results show that C-to-U conversion at position 4 in the potato mitochondrial tRNA(GAA)(Phe) is not required for aminoacylation,vith phenylalanine but is likely to be essential for efficient processing of this tRNA. [less ▲]

Characterization of the potato mitochondrial transcription unit containing 'native' trnS (GCU), trnF (GAA) and trnP (UGG)

in Plant Molecular Biology (1996), 30(3), 553-563

In order to identify the sequences promoting the expression of plant mitochondrial tRNA genes, we have characterized the trnS (GCU), trnF (GAA) and trnP (UGG) transcription unit of the potato ... [more ▼]

In order to identify the sequences promoting the expression of plant mitochondrial tRNA genes, we have characterized the trnS (GCU), trnF (GAA) and trnP (UGG) transcription unit of the potato mitochondrial genome. These three tRNA genes were shown to be co-transcribed as a 1800 nt long primary transcript. The transcription initiation site located 305 to 312 nt upstream of trnS is surrounded by a purine-rich region but does not contain the consensus motif proposed as a promoter element in dicotyledonous plants. Differential labelling of potato mitochondrial RNA with either guanylyltransferase or T4 polynucleotide kinase suggests that this site corresponds to the unique functional region responsible for the transcription of these three tRNA genes. The initiation site recently found upstream of Oenothera mitochondrial rr trnF does not seem to be used in potato mitochondria, although a very similar sequence is present 317 nt upstream of the corresponding potato gene. Major processing sites were identified at the 3' end of each tRNA gene. Another processing site, surrounded by a double hairpin structure, is located 498 nt downstream of trnP in stretch of 10 A residues. As judged from northern experiments, this region is close to the determination site of this transcription unit. [less ▲]

Genetic Mapping of Mitochondrial Markers by Recombinational Analysis in Chlamydomonas Reinhardtii

in Molecular & General Genetics [=MGG] (1995), 249(2), 185-90

The mitochondrial genome of Chlamydomonas reinhardtii is a 15.8 kb linear DNA molecule present in multiple copies. In crosses, the meiotic products only inherit the mitochondrial genome of the mating type ... [more ▼]

The mitochondrial genome of Chlamydomonas reinhardtii is a 15.8 kb linear DNA molecule present in multiple copies. In crosses, the meiotic products only inherit the mitochondrial genome of the mating type minus (paternal) parent. In contrast mitotic zygotes transmit maternal and paternal mitochondrial DNA copies to their diploid progeny and recombinational events between molecules of both origins frequently occur. Six mitochondrial mutants unable to grow in the dark (dk- mutants) were crossed in various combinations and the percentages of wild-type dk+ recombinants were determined in mitotic zygotes when all progeny cells had become homoplasmic for the mitochondrial genome. In crosses between strains mutated in the COB (apocytochrome b) gene and strains mutated in the COX1 (subunit 1 of cytochrome oxidase) gene, the frequency of recombination was 13.7% (+/- 3.2%). The corresponding physical distance between the mutation sites was 4.3 kb. In crosses between strains carrying mutations separated by about 20 bp, a recombinational frequency of 0.04% (+/- 0.02%) was found. Two other mutants not yet characterized at the molecular level were also used for recombinational studies. From these data, a linear genetic map of the mitochondrial genome could be drawn. This map is consistent with the positions of the mutation sites on the mitochondrial DNA molecule and thereby validates the method used to generate the map. The frequency of recombination per physical distance unit (3.2% +/- 0.7% per kilobase) is compared with those obtained for other organellar genomes in yeasts and Chlamydomonas. [less ▲]

Transmission et recombinaison du génome mitochondrial chez l'algue verte unicellulaire Chlamydomonas reinhardtii

Doctoral thesis (1993)

Transmission, recombinaison et conversion de marqueurs mitochondriaux chez Chlamydomonas

Scientific conference (1993)

Transmission, Recombination and Conversion of Mitochondrial Markers in Relation to the Mobility of a Group I Intron in Chlamydomonas

in Current Genetics (1993), 23(5-6, May-Jun), 518-25

Mitochondrial DNA transmission has been analyzed in diploids produced from sexual crosses or artificial fusions between Chlamydomonas strains which differ by several genetic markers: a group I intron (Cs ... [more ▼]

Mitochondrial DNA transmission has been analyzed in diploids produced from sexual crosses or artificial fusions between Chlamydomonas strains which differ by several genetic markers: a group I intron (Cs cob. 1 or alpha intron), three restriction sites (Nh, Nc and H markers) located 0.5-5 kb from the insertion site of the intron, and a MUD2 point mutation (27 bp from the insertion site) conferring resistance to myxothiazol. Recombination between mitochondrial markers is a general property of all crosses and fusions analyzed. In crosses between two intron-containing (alpha+) strains or two intron-less (alpha-) strains, the transmission is preferentially paternal (mt-), with a preponderance depending on the nature of the parental genomes. In crosses between alpha+ and alpha- strains, the conversion of intron-less molecules intron+ is frequent when the alpha+ parent is maternal (mt+) and nearly absolute when the alpha+ parent is paternal (mt-). In 94% of cases, the conversion is accompanied by the co-conversion of the MUD2 marker. In both crosses and artificial fusions, the conversion of alpha- into alpha+ also influences the transmission of the more distant Nh, Nc and H markers. It is hypothesized that the more frequent transmission of the genome containing the intron results from the elimination of alpha- molecules, as a result of a double-strand cut which is induced by an endonuclease encoded by the intron. [less ▲]

Mitochondrial Genome Transmission in Chlamydomonas Diploids Obtained by Sexual Crosses and Artificial Fusions: Role of the Mating Type and of a 1 Kb Intron

in Molecular & General Genetics [=MGG] (1990), 223(2), 180-4

The linear mitochondrial DNAs of the two infertile algal species Chlamydomonas smithii and C. reinhardtii are co-linear with the exception of a 1 kb intron (alpha intron) located in the cytochrome b gene ... [more ▼]

The linear mitochondrial DNAs of the two infertile algal species Chlamydomonas smithii and C. reinhardtii are co-linear with the exception of a 1 kb intron (alpha intron) located in the cytochrome b gene of C. smithii. C. smithii also possesses an additional HpaI restriction site (H marker) located in the COXI gene, about 5 kb from the intron. In reciprocal crosses, C. smithii (H+ alpha +) x C. reinhardtii (H- alpha -), the alpha intron is transmitted to all diploid progeny, whereas the H marker is frequently transmitted either biparentally or paternally depending on whether the C. smithii parent is maternal (mt+) or paternal (mt-). In diploids resulting from artificial fusion between vegetative cells, the absolute transmission of alpha is accompanied by the frequent transmission of the H+ marker, irrespective of the mating type of the parental strains. Finally, in reciprocal crosses between C. smithii (H+ alpha +) and recombinant H- alpha + clones, the transmission of the H marker is predominantly paternal or biparental. These results allow us to conclude that (1) the alpha intron behaves as a group I intron whose unidirectional conversion influences the transmission of the H marker; and (2) the mt- paternal mitochondrial genome is transmitted more often than the mt+. The mating type has no effect in diploids obtained by artificial fusion. [less ▲]