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  • Saccharomyces cerevisiae  (10)
  • Physical Chemistry  (9)
  • Nicotiana plumbaginifolia  (6)
  • 1990-1994  (25)
  • 1
    ISSN: 1617-4623
    Keywords: Mutagenized seeds ; Nicotiana plumbaginifolia ; Ethanol selection ; Alcohol dehydrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Six independent mutant lines ofNicotiana plumbaginifolia resistant to ethanol, designated E3, E8, E101, E112, E144 and E251, were isolated as germinating seedlings on selective medium. In all cases, resistance to ethanol was conferred by a single recessive nuclear mutation at the same locus. Mutant seeds and pollen lacked detectable ADH activity, with the exception of E251 where a residual activity was detected. An antiserum directed againstArabidopsis thaliana ADH detected an ADH-related polypeptide of 44 kDa present in wild-type seeds and, to a lesser extent, in the seeds of the leaky mutant E251. No ADH-related polypeptide could be detected in seeds of the other mutants. However, all of them had a nearly normal level of ADH mRNA except one which did not synthesize any mRNA. These results suggest that these ethanol-resistant mutants are impaired in one of the structural genes coding for alcohol dehydrogenase. The corresponding locus has been designatedAdh1.
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  • 2
    ISSN: 1617-4623
    Keywords: Nicotiana plumbaginifolia ; Nicotiana tabacum ; GATA-binding factor ; Nitrate reductase ; PCR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In higher plants, the expression of the nitrate assimilation pathway is highly regulated. Although the molecular mechanisms involved in this regulation are currently being elucidated, very little is known about the trans-acting factors that allow expression of the nitrate and nitrite reductase genes which code for the first enzymes in the pathway. In the fungus Neurospora crassa, nit-2, the major nitrogen regulatory gene, activates the expression of unlinked structural genes that specify nitrogen-catabolic enzymes during conditions of nitrogen limitation. The nit-2 gene encodes a regulatory protein containing a single zinc finger motif defined by the C-X2-CX17-C-X2-C sequence. This DNA-binding domain recognizes the promoter region of N. crassa nitrogen-related genes and fragments derived from the tomato nia gene promoter. The observed specificity of the binding suggests the existence of a NIT2-like homolog in higher plants. PCR and cross-hybridization techniques were used to isolate, respectively, a partial cDNA from Nicotiana plumbaginifolia and a full-length cDNA from Nicotiana tabacum. These clones encode a NIT2-like protein (named NTL1 for nit-2-like), characterized by a single zinc finger domain, defined by the C-X2-C-X18-C-X2-C amino acids, and associated with a basic region. The amino acid sequence of NTL1 is 60% homologous to the NIT2 sequence in the zinc finger domain. The Ntl1 gene is present as a unique copy in the diploid N. plumbaginifolia species. The characteristics of Ntl1 gene expression are compatible with those of a regulator of the nitrate assimilation pathway, namely weak nitrate inducibility and regulation by light.
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  • 3
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Cell cycle ; Bud site selection ; Guanine exchange factor ; Ras
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Guanine Exchange Factor (GEF) activity for Ras proteins has been associated with a conserved domain in Cdc25p, Sdc25p in Saccharomyces cerevisiae and several other proteins recently found in other eukaryotes. We have assessed the structure-function relationships between three different members of this family in S. cerevisiae, Cdc25p, Sdc25p and Bud5p. Cdc25p controls the Ras pathway, whereas Bud5p controls bud site localization. We demonstrate that the GEF domain of Sdc25p is closely related to that of Cdc25p. We first constructed a thermosensitive allele of SDC25 by specifically altering amino acid positions known to be changed in the cdc25-1 mutation. Secondly, we constructed three chimeric genes from CDC25 and SDC25, the products of which are as active in the Ras pathway as are the wild-type proteins. In contrast, similar chimeras made between CDC25 and BUD5 lead to proteins that are inactive both in the Ras and budding control pathways. This difference in the ability of chimeric proteins to retain activity allows us to define two subclasses of structurally different GEFs: Cdc25p and Sdc25p are Ras-specific GEFs, and Bud5p is a putative GEF for the Rsr1/Bud1 Rap-like protein.
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  • 4
    ISSN: 1617-4623
    Keywords: Tobacco ; Nicotiana plumbaginifolia ; Nitrate reductase deficient mutants ; Functional complementation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The homeologous nitrate reductase (NR) structural genes from tobacco were used to complement nitrate reductase deficient mutants from tobacco and Nicotiana plumbaginifolia. A plasmid conferring kanamycin resistance and lambda genomic clones carrying the tobacco wild-type alleles of the genes were co-electroporated in protoplasts of the tobacco mutant. Among 266 plants regenerated from kanamycin resistant colonies, 3 were able to grow permanently on a medium containing nitrate as sole nitrogen source. One of these three plants was further characterized. The ability to grow on nitrate was transmitted as a new single Mendelian dominant marker linked to kanamycin resistance. Molecular analysis of this clone confirmed the integration of a copy of the wild-type allele, and the synthesis at a low level of an active NR. This NR activity is sufficient to regulate both exogenous wild-type and endogenous mutated alleles of the genes at the transcriptional level. A N. plumbaginifolia mutant carrying a mutation impairing NR mRNA production was transformed by Agrobacterium mediated transfer of the wild-type tobacco nia-2 gene cloned into a binary vector. Similarly, kanamycin resistant calli were tested for their ability to grow on nitrate. Among 70 kanamycin resistant transformants, 7 were restored for nitrate assimilation. Molecular analysis revealed the integration of the tobacco gene, and the synthesis at a low level of the NR mRNA and of a nitrate inducible active NR.
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  • 5
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Translation ; Splicing ; Paromomycin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The MSS51 gene product has been previously shown to be involved in the splicing of the mitochondrial pre-mRNA of cytochrome oxidase subunit I (COX1). We show here that it is specifically required for the translation of the COX1 mRNA. Furthermore, the paromomycin-resistance mutation (P inf454 supR ) which affects the 15 S mitoribosomal RNA, interferes, directly or indirectly, with the action of the MSS51 gene product. Possible roles of the MSS51 protein on the excision of COX1 introns are discussed.
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  • 6
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Cell cycle ; Proline ; DNA sequencing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report here the isolation of temperature-sensitive mutants of the yeast Saccharomyces cerevisiae which exhibit cdc phenotypes. The recessive mutations defined four complementation groups, named ore1, ore2, ore3 and ore4. At the non-permissive temperature, strains bearing these mutations arrested in the G1 phase of the cell cycle. The wild-type allele of the gene altered in ore2 mutants was cloned. The nucleotide sequence of a fragment which can complement the mutation showed the presence of an open reading frame capable of encoding a protein with 286 amino acid residues. The deduced amino acid sequence showed 25% identity with that of the Escherichia coli Δ1-pyrroline-5-carboxylate reductase, an enzyme of the pathway for the biosynthesis of proline. The ore2 mutants, correspondingly, were found to be capable of growing at the non-permissive temperature on a synthetic medium supplemented with proline. In addition, the chromosomal location of the gene and its restriction map were compatible with those previously reported for the PRO3 gene which encodes the S. cerevisiae Δ1-pyrroline-5-carboxylate reductase.
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  • 7
    ISSN: 1617-4623
    Keywords: Transposable element ; Nitrate reductase ; Nicotiana plumbaginifolia ; γ-Ray mutagenesis ; Nucleotide sequence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract By Northern blot analysis of nitrate reductase-deficient mutants of Nicotiana plumbaginifolia, we identified a mutant (mutant D65), obtained after γ-ray irradiation of protoplasts, which contained an insertion sequence in the nitrate reductase (NR) mRNA. This insertion sequence was localized by polymerase chain reaction (PCR) in the first exon of NR and was also shown to be present in the NR gene. The mutant gene contained a 565 by insertion sequence that exhibits the sequence characteristics of a transposable element, which was thus named dTnp1. The dTnp1 element has 14 by terminal inverted repeats and is flanked by an 8-bp target site duplication generated upon transposition. These inverted repeats have significant sequence homology with those of other transposable elements. Judging by its size and the absence of a long open reading frame, dTnp1 appears to represent a defective, although mobile, transposable element. The octamer motif TTTAGGCC was found several times in direct orientation near the 5′ and 3′ ends of dTnp1 together with a perfect palindrome located after the 5′ inverted repeat. Southern blot analysis using an internal probe of dTnp1 suggested that this element occurs as a single copy in the genome of N. plumbaginifolia. It is also present in N. tabacum, but absent in tomato or petunia. The dTnp1 element is therefore of potential use for gene tagging in Nicotiana species.
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  • 8
    ISSN: 1617-4623
    Keywords: Mutagenized seeds ; Nicotiana plumbaginifolia ; Auxin-resistant mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutant lines of Nicotiana plumbaginifolia resistant to the synthetic auxins 1-naphthaleneacetic acid (NAA) and indole-3-butyric acid (IBA) were isolated as germinating seedlings on selective medium. In each case, resistance was conferred by a single recessive nuclear mutation at one of 3 loci designated iba1, iba2 and iba3. Labelling studies with 14C NAA suggest that resistance was not due to changes in the uptake or metabolism of NAA. Plants homozygous for the iba1 mutation exhibit a syndrome of atypical germination and growth suggestive of a defect in the biosynthesis, metabolism or localization of abscisic acid. Wild-type seeds treated with gibberellin exhibit the same syndrome, including resistance to NAA and IBA. On the basis of these observations, we propose that auxin toxicity in seeds may be mediated by a block in gibberellin biosynthesis.
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  • 9
    ISSN: 1617-4623
    Keywords: Nitrate reductase ; Reporter gene ; Nicotiana tabacum ; Nicotiana plumbaginifolia ; Transgenic plant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Reporter gene techniques and mutant analysis were used to identify the molecular basis of the regulation of the expression of nitrate reductase (NR) by nitrate and nitrate-, or ammonium-derived metabolites (N-metabolites), in the true diploïd species Nicotiana plumbaginifolia and in the amphidiploïd species Nicotiana tabacum. The N. plumbaginifolia mutant E23 results from the insertion of a Tnt1-like retrotransposon (Tnp2) in the first exon of the single-copy nia gene, which encodes nitrate reductase. One of the resulting transcripts ends in the 5′ LTR (long terminal repeat) sequence of this retrotransposon, and another one in the 3′ LTR. Nitrate and N-metabolites modulate the expression of these truncated transcripts, indicating that intron splicing and termination processes are not essential to these regulatory events. A GUS reporter sequence was transcriptionally linked to the promoter of the nia-1 gene of N. tabacum. This fusion was functional in transient expression assays done with protoplasts derived from mesophyll cells of N. tabacum. However none of the regulatory mechanisms known to affect steady-state levels of the nia-1 transcript were operative under these experimental conditions. Transgenic plants carrying either this fusion or translational fusions of GUS linked to the promoter of either the nia-1 or nia-2 gene of N. tabacum were obtained by Agrobacterium-mediated transfer. A low proportion of the transgenic plants (22 out of 105 independent transformants) expressed GUS activity although at a low level. Only 4 plants exhibited a detectable level of GUS mRNA. The concentration of this mRNA increased significantly in an NR-deficient background, indicating regulation by N-metabolites. Only 2 plants, however, showed regulation (induction) by nitrate. Attempts to use aux2 or nptII reporter sequences linked to either the nia-1 or nia-2 promoter as marker genes for the selection of regulatory mutants of the nitrate assimilation pathway were unsuccessful because of our inability to isolate transgenic plants in which these reporter genes were properly regulated by nitrate. The implications of these results are discussed.
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  • 10
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An infrared spectroscopic study of the 1 : 1 hydrogen-bond association of amidates with both methanol and 4-fluorophenol showed that the site of complexation is the oxygen of the amidate function. However the formamidate HCON2Me3 forms a second 1 : 1 complex on the nitrogen of the amidate. The formation constants of the hydrogen-bond complexes of the amidates with the reference hydrogen-bond donor 4-FC6H4OH indicate that the amidates are stronger hydrogen-bond bases than are amides and amide vinylogues. As such, the amidates constitute the strongest carbonyl bases hitherto investigated on the hydrogen-bond basicity scale.
    Additional Material: 5 Ill.
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