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A Jacquier

Publications and source records attributed to A Jacquier.

At least 19 recordsLinked to original sources
PubMed1992

Sequence of a 10.7 kb segment of yeast chromosome XI identifies the APN1 and the BAF1 loci and reveals one tRNA gene and several new open reading frames including homologs to RAD2 and kinases.

We report here the DNA sequence of a segment of chromosome XI of Saccharomyces cerevisiae extending over 10.7 kb. The sequence was determined using a double-strand sequencing strategy adapted from the random-clone strategy. The segment contains seven non-overlapping long open reading frames, YKL500, 505, 510, 513, 516, 518 and 520 and one tRNA gene. YKL505 and YKL513 are two already sequenced genes, the BAF1/ABF1 and the APN1 genes, respectively. YKL510 exhibits a strong homology to the RAD2 protein and YKL516 is presumably a protein kinase.

Amino Acid Sequence↗
PubMed1991

Splice site selection and role of the lariat in a group II intron.

The structural elements involved in 5' and 3' splice site (SS) selection in a group II intron were analyzed. While 5' SS selection appears to be defined by only one element, the EBS1-IBS1 pairing, four distinct structural components contribute to 3' SS selection, one of which being analogous to the "internal guide sequence" described for group I introns. Moreover, some of the mutants analyzed during this study induce efficient 5' SS hydrolysis and suggest how 5' SS transesterification is selected against hydrolysis. Finally, the lariat structure was found to accelerate both steps of splicing, suggesting that it "locks" the ribozyme in an active configuration.

Base Sequence↗
PubMed1990

Base-pairing interactions involving the 5' and 3'-terminal nucleotides of group II self-splicing introns.

By combining comparative sequence analyses and nucleotide replacements, we show that formation of the active center of group II introns rests in part on two novel long-range base-pairing interactions. (1) The last nucleotide of group II introns forms a solitary Watson-Crick base-pair with one of the nucleotides in the short sequence stretch connecting domains II and III. Formation of this base-pair is rate-limiting for the 3' cleavage and ligation step. (2) Nucleotides 3 and 4 form base-pairs with two consecutive nucleotides in a well-conserved internal loop of domain I. This interaction is involved in both the 5' and 3' cleavage steps. Possible relationships between group II and nuclear pre-mRNA introns are reassessed by taking into account these new pieces of information.

Bacteriophages↗
PubMed1990

Self-splicing group II and nuclear pre-mRNA introns: how similar are they?

The splicing pathway of pre-mRNA introns bears similarities to that of the group II introns, some members of which undergo self-splicing. The snRNAs may provide the pre-mRNA introns with RNA structures in trans comparable to those available in cis in group II introns. This article examines the available evidence for the hypothesis that the catalysis of these two splicing pathways is fundamentally equivalent.

Animals↗
PubMed1987

Multiple exon-binding sites in class II self-splicing introns.

Partial deletion of the exon 5' to S. cerevisiae intron a5, a self-splicing mitochondrial class II intron, reveals the existence of several sites of intron-exon interaction. We have identified two of the corresponding exon-binding sites in intron a5 by comparative sequence analysis and RNAase H digestion of the intron complexed to a DNA version of its 5' exon. Introduction of mutations in either the intronic sites or the complementary exonic sequences affects splicing in vitro, whereas double mutants in which intron-exon pairings have been restored show normal activity. Some of the mutants accumulate a product that was shown to be the intron-3' exon lariat, a postulated splicing intermediate. The possible role of one of the intronic sites in aligning exons for the ligation step is discussed.

Base Sequence↗
PubMed1986

Efficient trans-splicing of a yeast mitochondrial RNA group II intron implicates a strong 5' exon-intron interaction.

The reaction mechanism for self-splicing introns requires the existence of a 5' exon binding site on the intron. Experimental evidence is now presented consistent with the existence of such a binding site by demonstrating efficient and accurate trans-self-splicing of a yeast mitochondrial group II intron. Partial and complete trans-splicing reactions take place in the absence of branch formation, part of the usual pathway of nuclear splicing and group II self-splicing. In addition to indicating the existence of a 5' exon binding site on the intron, the results have mechanistic implications for group II self-splicing and perhaps for nuclear splicing as well.

Exons↗
PubMed1986

Universal code equivalent of a yeast mitochondrial intron reading frame is expressed into E. coli as a specific double strand endonuclease.

The intron of the mitochondrial 21S rRNA gene of Saccharomyces cerevisiae (r1 intron) possesses a 235 codon long internal open reading frame (r1 ORF) whose translation product determines the duplicative transposition of that intron during crosses between intron-plus strains (omega+) and intron-minus ones (omega-). Using site-directed mutagenesis, we have constructed a universal code equivalent of the r1 ORF that, under appropriate promoter control, allows the overexpression in E. coli of a protein identical to the mitochondrial intron encoded "transposase". This protein exhibits a double strand endonuclease activity specific for the omega- site. This finding demonstrates, for the first time, the enzymatic activity of an intron encoded protein whose function is to promote the spreading of that intron by generating double strand breaks at a specific sequence within a gene.

Amino Acid Sequence↗
PubMed1986

Mitochondrial introns as mobile genetic elements: the role of intron-encoded proteins.

Introns of organelle genes share distinctive RNA secondary structures that allow their classification into two known families. These structures are believed to play an essential role in splicing, and members of both structural classes have recently been shown to perform self-splicing reactions in vitro. In lower eukaryotes, many structured introns also contain long internal open reading frames (ORFs), which are able to code for hydrophilic proteins. Several properties of self-splicing structured introns suggest that they resemble mobile genetic elements, even though no actual transposition event involving these introns has yet been found. We report here on the characterization of two intron-encoded proteins that strongly support this attractive idea. First, we show that the class I intron of the 21S ribosomal RNA (rRNA) gene of Saccharomyces cerevisiae omega+ strains (rl intron) encodes a specific transposase. This protein has been partially purified from Escherichia coli cells that overexpress it from an artificial universal code equivalent to the rl intronic ORF. The omega transposase shows a double-strand endonuclease activity in vitro. This activity creates a 4-bp staggered cut with 3' OH overhangs within a specific sequence of the 21S rRNA gene of omega- strains. It is precisely within this sequence that the rl intron inserts by a duplicative transposition. Second, we report on the synthesis, in E. coli, of a putative reverse transcriptase encoded by the class II intron of the cytochrome b gene of Schizosaccharomyces pombe. This synthesis was obtained from E. coli expression vectors, using the class II intronic ORF linked to an artificial initiator sequence. As further support of the idea that structured introns are mobile, we show, from a systematic screening of introns in various yeast species, that the rl intron has transposed into the ATPase subunit 9 gene of Kluyveromyces fragilis. Structural features observed at the new intron homing site may be relevant to the transposition event.

Adenosine Triphosphatases↗
PubMed1986

RNA splicing and intron turnover are greatly diminished by a mutant yeast branch point.

Two mutant genes, both of which contain an A----C transversion at the absolutely conserved branch point of the yeast "TACTAAC box" (TACTAAC----TACTACC), were constructed and introduced into yeast cells. Splicing and gene expression are almost completely eliminated by this mutation, but a low level (approximately equal to 0.1%) of proper splicing is detectable. Branch point mapping indicates that the mutant branch is formed at the normal location--i.e., to cytidine rather than adenosine. The mutant branch is also a very poor substrate for the HeLa cell debranching enzyme. Although splicing of the mutant transcripts is very poor, the cells contain a high level of mutant intron because these excised introns are remarkably stable. The results imply that the normal branch point is important not only for branch formation and splicing but also for intron turnover.

Base Sequence↗
PubMed1985

A quantitative analysis of the effects of 5' junction and TACTAAC box mutants and mutant combinations on yeast mRNA splicing.

We have introduced four point mutations into the 5' junction (GTATGT) and TACTAAC box of a yeast intron-containing gene coding for beta-galactosidase. To analyze quantitatively mutant combinations, we deliberately avoided nucleotides adjacent to the sites of cleavage (GTATGT) and lariat formation (TACTAAC) and chose positions with expected weak effects on splicing. All four mutants do not affect, or only marginally affect, gene expression. The levels of precursor RNA and intermediates indicate, however, that splicing efficiency is affected in all cases; the first stage of splicing, 5' cleavage and lariat formation, is reduced two to 15-fold in these four mutants. The mutants were combined to generate compensatory and noncompensatory double mutant combinations. No evidence for a specific base-pairing interaction between the 5' junction and TACTAAC box could be obtained. The results suggest that all conserved positions in the 5' junction and TACTAAC box play a role in splicing efficiency.

Base Sequence↗
PubMed1985

An intron-encoded protein is active in a gene conversion process that spreads an intron into a mitochondrial gene.

The intron of the mitochondrial 21S rRNA gene of Saccharomyces cerevisiae possesses a long internal reading frame (ORF) that is conserved in various yeast species. In crosses between intron-plus and intron-minus variants, this intron determines a specific gene conversion phenomenon, which results in the integration of the intron sequence within all previously intron-minus copies of the gene. We show, from a frameshift mutant within the intron ORF and from the need of mitochondrial protein synthesis, that ORF encodes a protein active in the gene conversion that spreads the intron within populations of interbreeding strains. This new intron function is reminiscent of the "transposase" encoded by mobile genetic elements and is discussed in relation to other intron functions.

Base Sequence↗
PubMed1985

Biochemical identification and phylogenetic relationships in free-living amoebas of the genus Naegleria.

Using isoelectric focusing, the zymograms of 23 pathogenic and nonpathogenic Naegleria strains were studied for the activity of 16 enzymes. Certain enzymes (lactate dehydrogenase, L-threonine dehydrogenase, superoxide dismutase, acid phosphatase, malic enzyme, and leucine aminopeptidase) proved particularly useful from a practical point of view as they allow easy and reliable identification of pathogenic N. fowleri and N. australiensis as well as nonpathogenic N. lovaniensis strains. Genetic interpretation of these zymograms gave estimates of genetic distances that largely confirmed the taxonomic position of the Naegleria species. In addition, the genetic data suggest that there are two main phylogenetic groups in the genus Naegleria.

Amoeba↗
PubMed1984

Complexes of serum gamma-glutamyltransferase with apolipoproteins and immunoglobulin A.

We have detected complexes between gamma-glutamyltransferase and apolipoproteins or immunoglobulin A in sera from patients with hepatobiliary diseases but not in sera from healthy individuals. An average of 52.4% of the enzymic activity was precipitated by antiserum against apolipoprotein A, 29.9% by antiserum against apolipoprotein B, and 9.7% by antiserum against immunoglobulin A. Fifty to 60% of the enzyme activity was inhibited in the immunoprecipitates from the transferase fraction bound to apolipoprotein A or immunoglobulin A, and 21% in the fraction bound to apolipoprotein B. We identified the complexed transferase fractions by electrophoresis.

Aged↗
PubMed1984

Associations between serum gamma-glutamyltransferase and apolipoproteins: relationships with hepatobiliary diseases.

We studied the association between gamma-glutamyltransferase (GGT) and apolipoproteins A or B in serum of 42 patients with various hepatobiliary diseases. Binding of the enzyme to apolipoprotein A is not related to a clearly defined disease, but appears to be mainly influenced by the ratio of total cholesterol to GGT activity. An important fraction of GGT activity is associated with apolipoprotein B in patients with icteric or anicteric cholestasis. Conversely, in noncholestatic patients, the percentage of apolipoprotein B-bound GGT activity is low. Addition of the "heavy" form of GGT, obtained by solubilizing the membrane-bound enzyme with detergents, to a serum with low GGT activity led to the binding of the enzyme only to apolipoprotein A. The "light" form of GGT, obtained by limited proteolysis of the "heavy" form and added to the same serum, did not bind to either apolipoprotein A or apolipoprotein B. Thus, the association between the serum enzyme and apolipoprotein A apparently results from nonspecific aggregation of the amphiphilic "heavy" form of the enzyme. The origin of the apolipoprotein B-GGT complexes found in cholestatic patients needs further investigation.

Adult↗
PubMed1983

The intron of the mitochondrial 21S rRNA gene: distribution in different yeast species and sequence comparison between Kluyveromyces thermotolerans and Saccharomyces cerevisiae.

We have screened numerous different yeast species for the presence of sequences homologous to the intron of the mitochondrial 21S rRNA gene of Saccharomyces cerevisiae (intron r1) and found them in all Kluyveromyces species, some of the Saccharomyces species and none of the other yeasts tested. We have determined the nucleotide sequence of the r1-intron in K. thermotolerans and compared it with that of S. cerevisiae. The two introns are inserted at the same position within the 21S rRNA gene. They contain homologous internal open reading frames (ORFs) initiated at the same AUG codon which can be aligned over their entire length. Several silent multi-substitutions indicate that these intronic ORFs represent selectively conserved functional genes. Other intron segments, on the contrary, reveal short blocks of extensive homology separated by non-homologous stretches and/or additions-deletions. Comparison of our two yeast r1-introns with equivalent introns of N. crassa and A. nidulans mitochondria reveals that introns with very similar RNA secondary structures can accommodate different types of ORFs.

Base Sequence↗
PubMed1982

[Contribution of per- and trans-endoscopic pH measurements to the exploration of the upper digestive tract (author's transl)].

Per- and trans-endoscopic pH measurements in the upper digestive tract have provided new and interesting data. Performed by the authors on a series of 314 patients, they showed that the gastric pH is seldom acid, even in duodenal ulcer, and is always alkaline in gastric ulcer and gastric carcinoma. Gastritis may be divided into two groups, depending on whether the pH is normal or hypoacid (4.5 in the antrum, 2.5 in the fundus). Biopsies demonstrated the presence of intestinal metaplasia and epithelial dysplasia in 57.8% of 83 patients with hypoacid gastritis. The method therefore constitutes a simple and reliable means of determining markers of precancerous lesions.

Esophagoscopy↗