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  • Articles  (806)
  • Mutation
  • 2005-2009  (593)
  • 1985-1989  (213)
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  • Articles  (806)
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  • 1
    Electronic Resource
    Electronic Resource
    Mechanisms of tetracycline and rifampicin resistance inBacteroides fragilis mutants obtained by ionizing radiation (1988)
    Springer
    Journal of industrial microbiology and biotechnology 3 (1988), S. 299-304 
    Details
    ISSN: 1476-5535
    Keywords: Anaerobe ; Antibiotic resistance ; Irradiation ; Mutation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Based on a dose-survival curve, a radiation dose of 3.99 C/kg was used to induce antibiotic-resistant mutants inBacteroides fragilis. Escherichia coli B/r membrane fragments were employed as a reducing agent. Antibiotic-resistant mutants ofB. fragilis were utilized to study the mechanism by which these organisms become resistant to selected chemotherapeutic agents. Decreased accumulation of tetracycline by resistant mutants ofB. fragilis suggests that the resistance to this antibiotic is associated with the outer membrane permeability. There is a marked difference in the inhibitory action of rifampicin on RNA polymerase activity in rifampicin-sensitive and-resistant strains ofB. fragilis. This enzyme is, therefore, the likely target for inhibition of bacterial growth in this anaerobe by rifampicin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01569530
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  • 2
    Electronic Resource
    Electronic Resource
    Growth ofZymomonas on lactose: Gene cloning in combination with mutagenesis (1989)
    Springer
    Journal of industrial microbiology and biotechnology 4 (1989), S. 19-27 
    Details
    ISSN: 1476-5535
    Keywords: Zymomonas mobilis ; Growth on lactose ; Cloning ; Mutation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Wild-type strains ofZymomonas mobilis have a limited substrate range of glucose, fructose and sucrose. In order to expand this substrate range, transconjugants ofZ. mobilis containing Lac+ plasmids have been constructed. Although β-galactosidase is expressed in such strains, they lack the ability to grow on lactose. We now report the development ofZ. mobilis strains capable of growth on lactose. This was achieved in two stages. First, a broad host range plasmid was constructed (pRUT102) which contained the lactose operon under the control of aZ. mobilis promoter plus genes for galactose utilization.Z. mobilis CP4.45 containing pRUT102 was then subjected to mutagenesis combined with continued selection pressure for growth on lactose. One strain,Z. mobilis SB6, produced a turbid culture that yielded 0.25% ethanol from 5% lactose (plus 2% yeast extract) in 15 days.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01569689
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  • 3
    Electronic Resource
    Electronic Resource
    Mutational analysis of the upstream activation site of yeast ribosomal protein genes (1989)
    Springer
    Current genetics 15 (1989), S. 247-251 
    Details
    ISSN: 1432-0983
    Keywords: Yeast ; Ribosomal protein gene ; Transcription activation ; Mutation ; Methylation interference
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Most ribosomal protein (rp-)genes in yeast are preceded by conserved sequence motifs that act as upstream transcription-activating sites (RPG box). These sequence elements have previously been shown to represent specific binding sites for a protein factor, TUF. Comparison of the various nucleotide elements identified so far indicates a remarkably high degree of variation in the respective sequences. On the other hand, a methylation interference study performed with one RPG box revealed close contact points with the TUF protein along the entire sequence. To investigate the sequence requirements of the RPG box, we inserted synthetic oligonucleotides that differed from the general consensus sequence ACACCCATACATTT at single positions into a deletion mutant of the L25 promoter that lacked its natural RPG elements. Transcription activity was estimated by Northern analyses of the cellular level of L25-galK hybrid transcripts. The results show that in the 3′ part of this sequence element single substitutions are allowed at all positions, in the 5′ part, however, the nucleotide requirements appear to be more stringent. In particular, the invariant C at position 5 of the consensus sequence is absolutely necessary for its enhancer function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00447039
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  • 4
    Electronic Resource
    Electronic Resource
    Selection againstdam methylation sites in the genomes of DNA of enterobacteriophages (1985)
    Springer
    Journal of molecular evolution 21 (1985), S. 317-322 
    Details
    ISSN: 1432-1432
    Keywords: dam Methylase ; 6-Methyladenine ; Daughter-strand repair ; Mutation ; Selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Postreplicative methylation of adenine inEscherichia coli DNA to produce G6m ATC (where6mA is 6-methyladenine) has been associated with preferential daughter-strand repair and possibly regulation of replication. An analysis was undertaken to determine if these, or other, as yet unknown roles of GATC, have had an effect on the frequency of GATC inE. coli or bacteriophage DNA. It was first ascertained that the most accurate predictions of GATC frequency were based on the observed frequencies of GAT and ATC, which would be expected since these predictors take into account preferences in codon usage. The predicted frequencies were compared with observed GATC frequencies in all available bacterial and phage nucleotide sequences. The frequency of GATC was close to the predicted frequency in most genes ofE. coli and its RNA bacteriophages and in the genes of nonenteric bacteria and their bacteriophages. However, for DNA enterobacteriophages the observed frequency of DNA enterobacteriophages the observed frequency of GATC was generally significantly lower than predicted when assessed by the chi square test. No elevation in the rate of mutation of6mA in GATC relative to other bases was found when pairs of DNA sequences from closely related phages or pairs of homologous genes from enterobacteria were compared, nor was any preferred pathway for mutation of6mA evident in theE. coli DNA bacteriophages. This situation contrasts with that of 5-methylcytosine, which is hypermutable, with a preferred pathway to thymine. Thus, the low level of GATC in enterobacteriophages is probably due not to6mA hypermutability, but to selection against GATC in order to bypass a GATC-mediated host function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02115649
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  • 5
    Electronic Resource
    Electronic Resource
    Rates of molecular evolution and the fraction of nucleotide positions free to vary (1989)
    Springer
    Journal of molecular evolution 29 (1989), S. 180-187 
    Details
    ISSN: 1432-1432
    Keywords: Divergence ; Mitochondrial DNA ; Molecular evolution ; Constraints ; Two-parameter model ; Evolutionary distance ; Evolution ; Mutation ; Neutral space ; Variable positions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Selective constraints on DNA sequence change were incorporated into a model of DNA divergence by restricting substitutions to a subset of nucleotide positions. A simple model showed that both mutation rate and the fraction of nucleotide positions free to vary are strong determinants of DNA divergence over time. When divergence between two species approaches the fraction of positions free to vary, standard methods that correct for multiple mutations yield severe underestimates of the number of substitutions per site. A modified method appropriate for use with DNA sequence, restriction site, or thermal renaturation data is derived taking this fraction into account. The model also showed that the ratio of divergence in two gene classes (e.g., nuclear and mitochondrial) may vary widely over time even if the ratio of mutation rates remains constant. DNA sequence divergence data are used increasingly to detect differences in rates of molecular evolution. Often, variation in divergence rate is assumed to represent variation in mutation rate. The present model suggests that differing divergence rates among comparisons (either among gene classes or taxa) should be interpreted cautiously. Differences in the fraction of nucleotide positions free to vary can serve as an important alternative hypothesis to explain differences in DNA divergence rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02100116
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  • 6
    Electronic Resource
    Electronic Resource
    The origin of mutant cells: mechanisms by whichSaccharomyces cerevisiae produces cells homoplasmic for new mitochondrial mutations (1985)
    Springer
    Current genetics 9 (1985), S. 627-640 
    Details
    ISSN: 1432-0983
    Keywords: Mitochondria ; Mutation ; Yeast ; Selection ; Random drift
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Haploid yeast cells have about 50 copies of the mitochondrial genome, and a mutational event is unlikely to affect more than one of these at a time. This raises the question of how such cells, or their progeny, become fixed (homoplasmic) for the mutant alele. We have tested the roles of six hypothetical mechanisms in producing erythromycin-resistant mutant cells: (i) random partitioning of mitochondrial genomes at cell division; (ii) intracellular selection for mtDNA molecules of one genotype; (iii) intracellular random drift of mitochondrial allele frequencies; (iv) intercellular selection for cells of a particular mitochondrial genotype; (v) induction of mitochondrial gene mutations by the antibiotic used to select mutants; and (vi) reduction in the number of mitochondrial genomes per cell by the antibiotic. Our experiments indicate that intracellular selection plays the major role in producing erythromycin-resistant mutant cells in the presence of the antibiotic. In the absence of the antibiotic, the combined effects of random drift and random partitioning are most important in determining the fate of new mutations, most of which are lost rather than fixed. Our experiments provide no evidence for mutation induction or ploidy reduction by erythromycin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00449815
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  • 7
    Electronic Resource
    Electronic Resource
    Fluoroacetamide resistance mutations in Chlamydomonas reinhardtii (1987)
    Springer
    Archives of microbiology 148 (1987), S. 8-13 
    Details
    ISSN: 1432-072X
    Keywords: Chlamydomonas reinhardtii ; Fluoroacetamide ; Fluoroacetate ; Acetamide ; Mutation ; Transport ; Urea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Acetamide, a nitrogen and carbon source for Chlamydomonas reinhardtii, is hydrolyzed by acetamidase to ammonium and acetate. It also induces urea pathway activities. Fluoroacetamide (F-acetamide) is toxic to wild-type through conversion to F-citrate, a respiratory inhibitor. Resistant mutants were selected on plates of F-acetamide plus urea. When tested on acetamide plates two mutant classes were obtained, acm+ (utilized acetamide as sole N source) and acm-. All acm+ isolates had acetamidase activity and were obligate phototrophs (i.e. “dark-diers”). Acm- isolates had either normal urea assimilation (ure+) or lacked all urea pathway activities, namely transport, urea carboxylase and allophanate hydrolase (ure-). Inheritance patterns for both types indicated single nuclear gene mutations. The acm- ure+ type presumably resulted from a defective acetamidase gene, and the acm- ure- strains might be regulatory gene mutants. Temperature conditional F-acetamide tolerant mutants were also obtained. Acetamidase extracted from one such strain was more thermolabile than the wild-type enzyme, indicating a mutation in the coding region. The hypothesis that acetamidase is involved in urea assimilation was not supported by the genetic and biochemical evidence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00429639
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  • 8
    Electronic Resource
    Electronic Resource
    Genetic load and its causes in long-lived plants (1988)
    Springer
    Trees 2 (1988), S. 195-203 
    Details
    ISSN: 1432-2285
    Keywords: Genetic load ; Plants ; Mutation ; Heterosis ; Inbreeding depression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Many long-lived plant taxa are characterized by relatively high genetic load levels. This genetic load is manifested as the proportion of offspring that are physiologically handicapped to various degrees. It is proposed that the majority of this load is mutational load and is a consequence of the higher per generation mutation rates that occur in long-lived plants. Higher per generation mutation rates are a result of the chemostat-like accumulation of mutations in the apical initials as the plant grows. Genetic load, therefore, is a function of the postzygotic accumulation of mutations as well as mutations inherited from previous generations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202374
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  • 9
    Electronic Resource
    Electronic Resource
    A model of weak selection in the infinite alleles framework (1986)
    Springer
    Journal of mathematical biology 24 (1986), S. 353-360 
    Details
    ISSN: 1432-1416
    Keywords: Ewens sampling formula ; Infinite allele models ; Mutation ; Weak selection ; Markov process
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Ewens (1972) proposed a model in the infinite allele framework for populations with neutrality of all alleles at a particular locus. This paper proposes a generalisation of Ewens' result for situations where there is a form of weak selection. The models considered here are continuous time, discrete state space Markov processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00275643
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  • 10
    Electronic Resource
    Electronic Resource
    On the maintenance of genetic variation: global analysis of Kimura's continuum-of-alleles model (1986)
    Springer
    Journal of mathematical biology 24 (1986), S. 341-351 
    Details
    ISSN: 1432-1416
    Keywords: Mutation ; Selection balance ; Global stability ; Genetic variance ; Functional analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Methods of functional analysis are applied to provide an exact mathematical analysis of Kimura's continuum-of-alleles model. By an approximate analysis, Kimura obtained the result that the equilibrium distribution of allelic effects determining a quantitative character is Gaussian if fitness decreases quadratically from the optimum and if production of new mutants follows a Gaussian density. Lande extended this model considerably and proposed that high levels of genetic variation can be maintained by mutation even when there is strong stabilizing selection. This hypothesis has been questioned recently by Turelli, who published analyses and computer simulations of some multiallele models, approximating the continuum-of-alleles model, and reviewed relevant data. He found that the Kimura and Lande predictions overestimate the amount of equilibrium variance considerably if selection is not extremely weak or mutation rate not extremely high. The present analysis provides the first proof that in Kimura's model an equilibrium in fact exists and, moreover, that it is globally stable. Finally, using methods from quantum mechanics, estimates of the exact equilibrium variance are derived which are in best accordance with Turelli's results. This shows that continuum-of-alleles models may be excellent approximations to multiallele models, if analysed appropriately.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00275642
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