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J Lazowska

Publications and source records attributed to J Lazowska.

At least 37 records · Page 2Linked to original sources
PubMed1992

Two homologous mitochondrial introns from closely related Saccharomyces species differ by only a few amino acid replacements in their Open Reading Frames: one is mobile, the other is not.

We have undertaken a comprehensive study of the gene conversion of all the mitochondrial introns of Saccharomyces capensis. The approach used involved the measurements of intron transmission amongst the progeny of crosses between a recipient strain (Saccharomyces cerevisiae intronless mitochondria) and various donor strains (Saccharomyces capensis, with various combinations of mitochondrial introns). We have shown that the S. capensis second intron (bi2 of cytochrome b gene) is extremely active as a donor in gene conversion whereas its homologous S. cerevisiae intron is not. Determination of sequence of the S. capensis intron demonstrates that it differs from that of the homologous S. cerevisiae intron (bi2) by a very small number of nucleotide substitutions.

Amino Acid Sequence↗
PubMed1992

The MRS1 gene of S. douglasii: co-evolution of mitochondrial introns and specific splicing proteins encoded by nuclear genes.

We have developed a rapid and simple methodology to locate yeast genes within cloned inserts, obtain partial sequence information, and construct chromosomal disruptions of these genes. This methodology has been used to study a nuclear gene from the yeast S. douglasii (a close relative of S. cerevisiae), which is essential for the excision of the mitochondrial intron aI1 of S. douglasii (the first intron in the gene encoding subunit I of cytochrome oxidase), an intron which is not present in the mitochondrial genome of S. cerevisiae. We have shown that this gene is the homologue of the S. cerevisiae MRS1 gene, which is essential for the excision of the mitochondrial introns bI3 and aI5 beta of S. cerevisiae, but is unable to assure the excision of the intron aI1 from the coxI gene of S. douglasii. The two genes are very similar, with only 13% nucleotide substitutions in the coding region, transitions being 2.5 times more frequent than transvertions. At the protein level there are 86% identical residues and 7% conservative substitutions. The divergence of the MRS1 genes of S. cerevisiae and S. douglasii, and the concomitant changes in the structure of their mitochondrial genomes is an interesting example of the co-evolution of nuclear and mitochondrial genomes.

Amino Acid Sequence↗
PubMed1991

Incipient mitochondrial evolution in yeasts. II. The complete sequence of the gene coding for cytochrome b in Saccharomyces douglasii reveals the presence of both new and conserved introns and discloses major differences in the fixation of mutations in evolution.

We have determined the complete sequence of the mitochondrial gene coding for cytochrome b in Saccharomyces douglasii. The gene is 6310 base-pairs long and is interrupted by four introns. The first one (1311 base-pairs) belongs to the group ID of secondary structure, contains a fragment open reading frame with a characteristic GIY ... YIG motif, is absent from Saccharomyces cerevisiae and is inserted in the same site in which introns 1 and 2 are inserted in Neurospora crassa and Podospora anserina, respectively. The next three S. douglasii introns are homologous to the first three introns of S. cerevisiae, are inserted at the same positions and display various degrees of similarity ranging from an almost complete identity (intron 2 and 4) to a moderate one (intron 3). We have compared secondary structures of intron RNAs, and nucleotide and amino acid sequences of cytochrome b exons and intron open reading frames in the two Saccharomyces species. The rules that govern fixation of mutations in exon and intron open reading frames are different: the relative proportion of mutations occurring in synonymous codons is low in some introns and high in exons. The overall frequency of mutations in cytochrome b exons is much smaller than in nuclear genes of yeasts, contrary to what has been found in vertebrates, where mitochondrial mutations are more frequent. The divergence of the cytochrome b gene is modular: various parts of the gene have changed with a different mode and tempo of evolution.

Amino Acid Sequence↗
PubMed1991

A new specific DNA endonuclease activity in yeast mitochondria.

Two group I intron-encoded proteins from the yeast mitochondrial genome have already been shown to have a specific DNA endonuclease activity. This activity mediates intron insertion by cleaving the DNA sequence corresponding to the splice junction of an intronless strain. We have discovered in mitochondrial extracts from the yeast strain 777-3A a new DNA endonuclease activity which cleaves the fused exon A3-exon A4 junction sequence of the CO XI gene.

Base Sequence↗
PubMed1989

Protein encoded by the third intron of cytochrome b gene in Saccharomyces cerevisiae is an mRNA maturase. Analysis of mitochondrial mutants, RNA transcripts proteins and evolutionary relationships.

We have established the nucleotide sequence of the wild-type and that of a trans-acting mutant located in the third (bi3) intron of the Saccharomyces cerevisiae mitochondrial cytochrome b gene. The intron, 1691 base-pairs long, has an open reading frame 1045 base-pairs long, in phase with the preceding exon and the mutation replaces the evolutionarily conserved Gly codon of the second consensus motif by an Asp codon and blocks the formation of mature cytochrome b mRNA. Splicing intermediates of 5300 and 3900 bases with unexcised bi3 intron and a characteristic novel polypeptide (p50), the size of which corresponds to the chimeric protein encoded by upstream exons and the bi3 intronic open reading frame (ORF), accumulate in this and other bi3 splicing-deficient mutants. We conclude that the protein encoded by the bi3 ORF is a specific mRNA maturase involved in the splicing of the cytochrome b mRNA. The open reading frame of the third intron is remarkably similar to that of the unique intron of the cytochrome b gene (cob A) of Aspergillus nidulans. Both are located in exactly the same position and possibly derive from a recent common ancestor by a horizontal transfer. We have established the nucleotide sequence of an exonic mutant located in the B3 exon. This missense mutation changes the Phe codon 151 into a Cys codon and leads to the absence of functional cytochrome b but does not affect splicing. Finally, we have studied the splicing pathway leading to the synthesis of cytochrome b mRNA by analysing, in a comprehensive manner, the 22 splicing intermediates of several mutants located in bi3.

Aspergillus nidulans↗
PubMed1988

Discrimination between different groups of Candida parapsilosis by mitochondrial DNA restriction analysis.

The analysis of mitochondrial DNA (mtDNA) from several strains of Candida parapsilosis and Candida rhagii by restriction endonucleases enabled us to discriminate between several groups within the C. parapsilosis species and to allocate laboratory strains to one of these. The mtDNAs isolated ranged in size from 20 to 31 kb. The mtDNA isolated from group 1 C. parapsilosis hybridises with both ATPase subunit 6 and 8 gene probes, the same restriction fragment hybridising with both probes.

Candida↗
PubMed1984

A yeast with linear molecules of mitochondrial DNA.

Mitochondrial DNA from the yeast strain SR23, tentatively allocated to the species Candida rhagii, consists of linear molecules 30 kb long. This has been demonstrated by restriction analysis and selective radioactive labelling of terminal restriction fragments. Preliminary sequence analysis indicated that the two ends of the molecule are formed by inverted repeats. The arrangement of several genes in the mitochondrial genome of C. rhagii SR23 was established by specific hybridisation with probes prepared from mitochondrial DNA of Saccharomyces cerevisiae. The arrangement is unique, with genes coding for the two ribosomal RNAs placed widely apart. Intron(s) may be present in the gene coding for cytochrome b.

Candida↗
PubMed1981

Splice points of the third intron in the yeast mitochondrial cytochrome b gene.

We report the nucleotide sequences at the splicing junctions of intron 13 of the cytochrome b (box) "long" gene of the mitochondrion of Saccharomyces cerevisiae and compare them with the homologous sequences in Aspergillus nidulans. The two introns occupy exactly the same position and display an open reading frame in phase with the preceding exon at the 5' end and a blocked region at the 3' end.

Base Sequence↗
PubMed1980

[New mechanism for regulation of genetic expression].

DNA sequence studies of mutated and wild type alleles of an intron in the mosaic mitochondrial gene for cytochrome b have revealed the possible existence of a protein coded in the intron and involved in RNA splicing. This protein would be endowed with properties of intrinsic autotomy of its own messenger RNA.

Amino Acid Sequence↗
PubMed1980

Sequence of introns and flanking exons in wild-type and box3 mutants of cytochrome b reveals an interlaced splicing protein coded by an intron.

We have determined the DNA sequence of the wild type and mutated introns as well as their flanking exons in the yeast mitochondrial gene specifying cytochrome b. The second intron (box3) encodes a trans-acting protein "mRNA maturase" responsible for splicing and maturation of cytochrome b mRNA. This protein is interlaced with cytochrome b exon sequences. Its biosynthesis is subject to a negative feedback which may constitute a regulatory mechanism for the expression of split genes.

Base Sequence↗
PubMed1979

Electron microscopic analysis of the yeast mitochondrial DNA segment conferring chloramphenicol resistance.

Mitochondrial DNAs from six p- mutants carrying the genetic locus Rib1 and deleted for the rest of the genome were analyzed. Distribution of circular molecules from one mutant followed exactly the frequency rule, l/n, for multimers with discreet classes n, 2n, 3n, etc. Another, genetically unstable mutant displayed a continuous spectrum of circular molecules of various lengths. Four other mutants contained multiple series of circular molecules. Partial denaturation maps show that the mutants analyzed show a common segment ca. 1.0 micron long and differ by characteristic deletions of extremites of this segment. Short terminal deletions of the right i.e. pointing towards the Rib3 locus, terminus of this segment are correlated with modifications of the recombination properties related to the omega locus.

Chloramphenicol↗
PubMed1976

Recombined molecules of mitochondrial DNA obtained from crosses between cytoplasmic petite mutants of Saccharomyces cerevisiae: the stoichiometry of parental DNA repeats within the recombined molecule.

We have studied recombination between repetitive mitochondrial DNAs from cytoplasmic petite mutants of Saccharomyces cerevisiae. Mitochondrial DNA was isolated from two parental p- mutants, carrying respectively the CR and the ER mitochondrial genetic markers, and from two p- CRER diploid genetic recombinants. These two recombinants, obtained from the same parental petites, differ in their degrees of suppressiveness. The p- mitochondrial DNAs were analyzed by DNA-DNA hybridization, high resolution melting and reassociation kinetics. It was found that the repeating unit of the CR parental p- DNA is 3 to 4 times longer than that of the ER parent. There is very little sequence homology between these two p- mitochondrial DNAs and almost all parental sequences are integrated into the recombined molecules. Mitochondrial DNA from both types of recombinants seems to contain the two parental repeating units in the ratio 1:1.

Base Sequence↗
PubMed1976

Electron microscopy of analysis of circular repetitive mitochondrial DNA molecules from genetically characterized rho- mutants of Saccharomyces cerevisiae.

1. We have studied mtDNA purified from nine p- petite mutants in which most of the wild type sequence has been deleted but the genetic markers conferring resistance to erythromycin of oligomycin or paromomycin have been retained. 2. All mtDNA contained numerous circular molecules. The size distribution of the circles conformed to a multimeric series which was characteristic for each mutant. We conclude that any one region of the wild type mtDNA molecule, when maintained in a p- clone, while other regions are deleted, can give rise to a multimeric series of circles. 3. In tandem straight repetitive mtDNAs the circles contain odd and even number of unit sequence repeats. In palindrome repetitive mtDNAs the circles contain mostly even number of unit sequence repeats. Thus, one straight or two inverted repeats constitute the monomeric unit of circularization. 4. We found that the frequency distribution of circles follows on a number basis a simple rule: frequency of numeric circles = 1/n frequency of monomeric circles, for n = 2, 3 and 4. Thus, on a mass basis each class represents the same fraction of total mtDNA and the mitochondrial genome has the same probability to constitute one monomeric circle or to be a part of n-meric circle. We interpret this finding that in vivo all molecules are circular. 5. Four mutants displayed a single multimeric series of circles ranging from 0.3 mum to 2.4 mum monomer circle length. Five mutants displayed multiple different multimeric series. In the latter case, the longest unit sequence repeat length was equal to the sum of the two shorter unit sequence repeat lengths. Sorting out, recombination and internal deletions of circular repetitive p- mtDNA molecules are discussed.

Centrifugation, Density Gradient↗