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  • 1990-1994  (5)
  • 1985-1989
  • 1994  (5)
  • Conidiation  (1)
  • H+-ATPase  (1)
  • Macrolide antibiotics  (1)
  • P19 cells  (1)
  • ZnO powder  (1)
  • 1
    ISSN: 1572-879X
    Keywords: microwave absorption ; electrical conductivity ; single crystal particles ; doped Si powders ; ZnO powder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A microwave absorption technique based on cavity perturbation theory is shown to be applicable for electrical conductivity measurements of both a small, single-crystal particle and finely divided powder samples whenσ values fall in either the low (σ〈0.1 Ω−1 cm−1) or the intermediate (0.1 ≤σ≤ 100 Ω−1 cm−1) conductivity region. The results here pertain to semiconductors in the latter region. If the skin depth of the material becomes significantly smaller than the sample dimension parallel to theE-field, an appreciable error can be introduced into the calculated conductivity values; however, this discrepancy is eliminated by correcting for the field attenuation associated with the penetration depth of the microwaves. A modification of this approach utilizing the skin depth allows a first-order correction to be applied to powder samples which results in the accurate measurement of absoluteσ values, and results with doped Si powders are compared toσ values obtained from one small single particle using this microwave technique as well as reported DCσ values determined with single crystals. The use of this microwave absorption technique with small particles having high surface/volume ratios, such as catalyst supports and oxide catalysts, under controlled environments can provide fundamental information about adsorption and catalytic processes on such semiconductor surfaces. An application to a ZnO powder demonstrates this capability.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0983
    Keywords: Conidiation ; Fungi ; brlA ; Microbial development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Conidiation in the filamentous ascomycete Aspergillus nidulans requires activation of brlA, a well-characterized transcriptional regulator of genes that are induced specifically during asexual development. We have isolated and characterized developmental mutations in six loci, designated fluG, flbA, flbB, flbC, flbD, and flbE, that result in defective development and reduced brlA expression. These mutants grow indeterminately to produce masses of aerial hyphae resulting in the formation of cotton-like colonies with a “fluffy” morphology. The results of growth and epistasis tests involving all pairwise combinations of fluffy mutations indicate complex hierarchical relationships among these loci. We discuss these genetic interactions and propose that there are multiple mechanisms for activating brlA.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 243 (1994), S. 225-233 
    ISSN: 1617-4623
    Keywords: Protein synthesis ; Translation ; Accuracy ; Macrolide antibiotics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Inaccurate protein synthesis produces unstable β-galactosidase, whose activity is rapidly lost at high temperature. Erythromycin, lincomycin, clindamycin, and celesticetin were shown to counteract the error-inducing effects of streptomycin on β-galactosidase synthesized in the antibiotic-hypersensitive Escherichia coli strain DB-11 Met −. Newly synthesized β-galactosidase was more easily inactivated by high temperatures when synthesized by bacteria partially starved for arginine, threonine, or methionine. Simultaneous treatment with erythromycin or linocomycin yielded β-galactosidase that was inactivated by high temperatures less easily than during starvation alone, an effect attributed to stimulation of ribosome editing. When synthesized in the presence of canavanine, β-galactosidase was inactivated by high temperature more easily but this effect could not be reversed by erythromycin. The first arginine in β-galactosidase occurs at residue 13, so the effect of erythromycin during arginine starvation is probably to stimulate dissociation of erroneous peptidyl-tRNAs of at least that length. Correction of errors induced by methionine starvation is probably due to stimulation of dissociation of erroneous peptidyl-tRNAs bearing peptides at least 92 residues in length. All the effects of erythromycin or the tested lincosamides on protein synthesis are probably the result of stimulating the dissociation from ribosomes of peptidyl-tRNAs that are erroneous or short.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-6881
    Keywords: H+-ATPase ; molecular modeling ; helical hairpin ; aromatic slipper ; coupling ; molecular dynamics ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract A molecular model for transmembrane segments 1 and 2 from the fungal proton pumping ATPase has been developed, and this structure is predicted to form a helical hairpin loop structure in the membrane. This region was selected because it is highly conformationally active and is believed to be an important site of action for clinically important therapeutics in related animal cell enzymes. The hairpin loop is predicted to form an asymmetric tightly packed structure that is stabilized by an N-cap between D140 and V142, by hydrogen bonding between residues in the turn region and the helices, and by π-π interactions between closely apposed aromatic residues. A short four-residue S-shaped turn is stabilized by hydrogen bonding but is predicted to be conformationally heterogeneous. The principal effect of mutations within the hairpin head region is to destabilize the local close packing of side groups which disrupts the pattern of hydrogen bonding in and around the turn region. Depending on the mutation, this causes either a localized or a more global distortion of the primary structure in the hairpin region. These altered structures may explain the effects of mutations in transmembrane segments 1 and 2 on ATP hydrolysis, sensitivity to vanadate, and electrogenic proton transport. The conformational sensitivity of the hairpin structure around the S-turn may also account for the effects of SCH28080 and possibly ouabain in blocking ATPase function in related animal cell enzymes. Finally, the model of transmembrane segments 1 and 2 serves as a template to position transmembrane segments 3 and 8. This model provides a new view of the H+-ATPase that promotes novel structure/function experimentation and could serve as the basis for a more detailed model of the membrane sector of this enzyme.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1058-8388
    Keywords: CRABP-I ; P19 cells ; DNA methylation ; Gene expression ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The mouse cellular retinoic acid binding protein-I (CRABP-I) gene is specifically up-regulated by retinoic acid (RA) in P19 mouse embryonal carcinoma cells, and its expression in animals is spatially and temporally restricted to RA-sensitive tissues during embryonic development. This study demonstrates that, in adult mouse tissues and P19 cells where the expression of CRABP-I is detected at the basal level, the 5′- flanking region of the CRABP-I gene is hypermethylated at the C residues of all the Hpa II sites. Conversely, in mouse embryos during early stages of development when the expression of CRABP-I gene is detected at a much higher level, this region is demethylated at these Hpa II sites. In P19, enhancement on the RA-induced up-regulation of CRABP-I can be observed in cells treated with 5-azacytidine (5-AzaC) in conjunction with RA, where partial demethylation in the 5′-flanking region of CRABP-I gene is observed. Nuclear run-on experiments indicate that increased message levels of CRABP-I in P19 cells can be accounted for, at least partially, by increases in its transcription rates. The induction of retinoic acid receptor (RAR) β by RA can also be enhanced by 5-AzaC, but to a much lesser degree. In contrast, all the Hpa II sites in the structural gene portion, at least in the first two exons, are fully demethylated at the C residues. © 1994 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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