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B Dujon

Publications and source records attributed to B Dujon.

108 records · Page 6Linked to original sources
PubMed1982

The hierarchical approach to the DNA stability problem. II. Some applications and speculations with yeast mitochondrial DNA as an example.

As discussed in the preceding article [1] hierarchical analysis of DNA sequences should make it possible to treat complex unfolding (and refolding) processes involving both equilibrium and non-equilibrium subtransitions. Hence a variety of actual experimental situations may be analyzed. This is demonstrated with the help of a 1950 bp yeast mitochondrial DNA sequence encompassing part of the 21S ribosomal RNA gene: excellent fit of complex denaturation and renaturation profiles is achieved with only two adjustable parameters. The advantage of dealing with objectively defined stability units is also apparent when stability profiles are compared to known functional maps: striking correlations may be brought out and their possible significance is briefly discussed.

Base Composition↗
PubMed1980

Sequence of the intron and flanking exons of the mitochondrial 21S rRNA gene of yeast strains having different alleles at the omega and rib-1 loci.

The complete nucleotide sequence has been determined for the intron, its junctions and the flanking exon regions of the 21S rRNA gene in three genetically characterized strains differing by their omega alleles (omega+, omega- and omega n) and by their chloramphenicol-resistant mutations at the rib-1 locus. Comparison of these DNA sequences shows that: --omega+ differs from omega- and omega n by the presence of the intron (1143 bp), as well as by a second and unexpected mini-insert (66 bp) located 156 bp upstream within the exon, whose nature and functions are still unknown but whose striking palindromic structure may suggest a mitochondrial transposable element. --The two mutations C321R and C323R correspond to two different monosubstitutions, 56 bp apart in the omega- and omega n strains but separated by the intron in the omega+ strains. In relation to previous genetic results, a model is discussed assuming that the interactions of two different regions or genetic loci determine the chloramphenicol resistance, one of which contains the omega n mutations. --A long uninterrupted coding sequence able to specify a 235 amino acid polypeptide exists within the intron. This remarkable observation gives new insight into the origin of the mitochondrial introns and raises the question of the possible functions of intron-encoded polypeptides. Finally, sequence comparisons with evolutionarily distant organisms, showing that different rRNA introns are inserted at different positions of an otherwise highly conserved region of the gene, suggest a recent insertion of these introns and a mechanism for splicing after the assembly of the large ribosomal subunit.

Alleles↗
PubMed1980

Replicator regions of the yeast mitochondrial DNA responsible for suppressiveness.

Hypersuppressiveness is a heritable property of some rho- mutants (called HS) that, in crosses to rho+, give rise to about 100% rho- cells. The mtDNAs of all HS rho- mutants reveal a common organization: they all share a homologous region of about 300 base pairs (called rep) and the fragments retained are always short (ca. 1% of the wild-type genome) and tandemly repeated. Using one HS rho- mutant as an example, we show that, after crosses with rho+ strains, the mitochondrial genome of the progeny is indistinguishable from that of the HS parent. This suggests that HS mtDNA molecules have a decisive selective advantage for replication during the transient heteroplasmic stage that follows zygote formation, the rep regions playing a role in the control of replication initiation of the mtDNA molecules. The complete nucleotide sequence of one HS rho- mutant and its localization in the oli1-rib3 segment of the rho+ mitochondrial genome are presented. Comparison of the nucleotide sequences of the rep regions of two different HS rho- mutants reveals that several rep sequences must exist in the wild-type genome, probably as a result of duplications of an originally unique ancestor.

Base Sequence↗
PubMed1979

Mutants in yeast affecting ethidium bromide induced rho- formation and their effects on transmission and recombination of mitochondrial genes.

A series of mutants called ebi, less inducible by ethidium bromide than the parental strain for the rho+ leads to rho- mutation have been isolated after E.M.S. mutagenesis. Some of the ebi mutants also show an important accumulation of rho- cells, in the absence of ethidium bromide. Ebi mutations are nuclearly inherited as shown by meiotic segregation. The effects of these mutants on the transmission and recombination of mitochondrial genes among the diploid progeny of crosses have been studied. Some of the ebi mutants show a non coordinated transmission of the oli1 mitochondrial marker with respect to other mitochondrial markers unexpected for homosexual crosses. This bias which is independent from omega will be discussed in relation to the segregation and recombination. No significant decrease of the frequency of recombinants has been detected.

Crosses, Genetic↗
PubMed1979

Genetic and physical characterization of a segment of yeast mitochondrial DNA involved in the control of genetic recombination.

Genetic recombination between the 3 RIB (ribosomal) loci of yeast mitochondrial DNA is under the control of a mitochondrial locus named omega (with alleles omega+ and omega-) which is tightly linked to the RIBI locus. We have attempted to elucidate the molecular mechanisms(s) involved by using rho- mutants with similar (RIBI+ RIB2+ RIB3(0) genotype but different recombination properties in rho- x rho+ crosses. These were obtained through pedigree analysis and their mitochondrial DNAs were mapped on a high resolution physical map of the RIB section that had been built by analysis of thermal denaturation profiles and electron microscopy of partially denatured molecules. By comparison of physical and genetic data it can be shown that possession of the omega+ allele by the rho- cell is not sufficient for its expression in crosses, some additional DNA segments(s) in the ribosomal region being needed. This result and several features of the rho+ x rho- crosses are discussed in the light of current concepts in mitochondrial genetics of yeast and the recently discovered fact that omega+ and omega- strains differ by the presence of a 1000 base pairs insertion in the former.

Base Sequence↗
PubMed1978

Detection of specific DNA sequences in yeast by colony hybridization.

A procedure is described for the detection of specific DNA sequences in Saccharomyces cerevisiae. This method allows a rapid screening of a large number of yeast colonies. The yeast cells of each colony, grown on nitrocellulose filters, are converted, in situ, to protoplasts by snail enzyme, and are then lysed and their DNAs are denatured and fixed on the filter. The presence of the specific DNA sequence is detected directly on the filter by hybridization with a radioactive cRNA. We have used successfully this technique to detect the presence or the absence of specific mt DNA sequences in p+, p- and p0 strains, and to detect the presence or the absence of the 2 mum DNA sequences in different strains.

Base Sequence↗
PubMed1976

Mitochondrial genetics. XI. Mutations at the mitochondrial locus omega affecting the recombination of mitochondrial genes in Saccharomyces cerevisiae.

1. A series of CS revertants has been selected from various strains (both omega+ and omega-) carrying a CR mitochondrial mutation at the RIB1 locus. The properties of mitochondrial recombination exhibited by these CS revertants in various crosses, have been examined systematically. The omega allele of the CS revertants has been defined in crosses with omega+ and omega- tester strains using two criteria: the polarity of recombination and a new criterium called relative output coefficient. We found that mutations of omega appear frequently associated with the mutations at the RIB1 locus selected from omega- strains but not with those selected from omega+ strains. A new allelic form of omega (omega n) which had not been found amongst wild type yeast strains is characterised. Similarly omega n mutation was found frequently associated with CR mutants at the RIB1 locus selected from omega- CS strains but not with those selected from omega+ CS strains. The omega n mutants, and the omega+ and omega- strains, explain the groups of polarity previously observed by Coen et al. (1970). 2. Main features of mitochondrial crosses with omega n strains (omega+ x omega n, omega- x omega n and omega n x omega n) are analysed. Recombination is possible between the different mitochondrial genetic markers. No high polarity of recombination is observed and the frequency of recombinants are similar to those found in homosexual crosses (omega+ x omega+ and omega- x omega-). A striking property, observed for the first time, exists in crosses between zota+ omega n CS strains and some zota- CREO mutants: the zota- CREO are unable to integrate by recombination their CR allele into the zota+ mit-DNA of omega n CS strains while being capable of integrating it into omega+ CS or omega- CS genomes. 3. It is proposed that the omega locus is the site of initiation of non reciprocal recombination events, the omega+/omega- pairing specifically initiates the non-reciprocal act while omega+/omega n or omega-/omega n pairings do not. 4. The molecular nature of the omega n mutation and its bearing on the structure of the omega locus are discussed. It is suggested that omega n mutations correspond to macrolesions (probably deletions) of a segment of the mit-DNA covering the omega and RIB1 loci. If omega n is a partial deletions of the omega- sequence the omega+ could be an additionnal deletion of the omega n sequence. 5. The occurrence of spontaneous CR and ER mitochondrial mutations has been analysed by the Luria and Delbrück fluctuation test in omega- and omega n isonuclear strains. Results of these tests indicate that an intracellular selection of resistant copies preexisting the action of the anttibiotic occurs.

Alleles↗
PubMed1974

Mitochondrial genetics. VI. The petite mutation in Saccharomyces cerevisiae: interrelations between the loss of the p+ factor and the loss of the drug resistance mitochondrial genetic markers.

The survival of the rho(+) factor and of Drug(R) mitochondrial genetic markers after exposure to ethidium bromide has been studied. A technique allowing the determination of Drug(R) genetic markers among a great number of both grande and petite colonies has been developed. The results have been analyzed by the target theory. The survival of the rho(+) factor is always less than the survival of any Drug(R) genetic marker. The survivals of C(R) and E(R) are similar to each other, while that of O(R) is greater than that of the other two Drug(R) markers. All possible combinations of Drug(R) markers have been found among the rho(-) petite cells induced, while the only type found among the grande colonies is the preexisting one. The loss of the C(R) and E(R) genetic markers was found to be the most frequently concomitant, while the correlation between the loss of the O(R) marker and the other two Drug(R) markers is less strong. Similar results have been obtained after U.V. irradiation. Interpretations concerning the structure of the yeast mitochondrial genome are given and hypotheses on the mechanism of petite mutation discussed.

Drug Resistance, Microbial↗
PubMed1974

Mitochondrial genetics. VII. Allelism and mapping studies of ribosomal mutants resistant to chloramphenicol, erythromycin and spiramycin in S. cerevisiae.

We have isolated 15 spontaneous mutants resistant to one or several antibiotics like chloramphenicol, erythromycin and spiramycin. We have shown by several criteria that all of them result from mutations localized in the mitochondrial DNA. The mutations have been mapped by allelism tests and by two- and three-factor crosses involving various configurations of resistant and sensitive alleles associated in cis or in trans with the mitochondrial locus omega which governs the polarity of genetic recombination. A general mapping procedure based on results of heterosexual (omega(+)x omega(-)) crosses and applicable to mutations localized in the polar segment is described and shown to be more resolving than that based on results of homosexual crosses. Mutations fall into three loci which are all linked and map in the following order: omega-R(I)-R(II)-R(III). The first locus is very tightly linked with omega while the second is less linked to the first. Mutations of similar resistance phenotype can belong to different loci and different phenotypes to the same locus. Mutations confer antibiotic resistance on isolated mitochondrial ribosomes and delineate a ribosomal segment of the mitochondrial DNA. Homo- and hetero-sexual crosses between mutants of the ribosomal segment and those belonging to the genetically unlinked ATPase locus, O(I), have been performed in various allele configurations. The polarity of recombination between R(I), R(II), R(III) and O(I) decreases as a function of the distance of the R locus from the omega locus rather than as a function of the distance of the R locus from the O(I) locus.

Adenosine Triphosphatases↗
PubMedDate not supplied

The complete sequence of the 8.2 kb segment left of MAT on chromosome III reveals five ORFs, including a gene for a yeast ribokinase.

We report here the DNA sequence of a segment of chromosome III extending over 8.2 kb. The sequence was determined using the random clone strategy followed by oligonucleotide-directed sequencing. The segment contains five long open reading frames, YCR521, 522, 523, 524 and 526, with only short distances between them. YCR523 (333 codons) encodes a ribokinase, a new function for yeast. YCR526 originates inside the MAT cassette, which is in continuity with the present segment, and extends over 358 codons outside of MAT. YCR524 (923 codons) codes for a putative membrane protein. YCR521, 522 and 524, have each been disrupted by insertion of a URA3 cassette and are non-essential genes. An active ARS element is located within YCR523 or its vicinity.

Base Sequence↗
PubMedDate not supplied

Trinucleotide repeats and other microsatellites in yeasts.

Microsatellites are direct tandem DNA repeats found in all genomes. A particular class of microsatellites, called trinucleotide repeats, is responsible for a number of neurological disorders in humans. We review here our current state of knowledge on trinucleotide repeat instability, and discuss the molecular mechanisms that may be involved in trinucleotide repeat expansions leading to fatal diseases in humans. We also present original data on microsatellite distribution in several microbial genomes, and on the use of microsatellites as physical markers to accurately and easily genotype yeast strains.

Bacteria↗