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  • Cell & Developmental Biology  (3)
  • GEOPHYSICS  (3)
  • alternative splicing  (2)
  • 1
    ISSN: 1573-5176
    Keywords: Chlorella sorokiniana ; NADP-specific glutamate dehydrogenase gene/mRNAs ; promoter ; alternative splicing ; cell wall ; sporopollenin ; carotenoid-biosynthesis inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chlorella sorokiniana may prove to be a useful organism in which to express genes/cDNAs from certain higher plants encoding enzymes catalyzing the synthesis of compounds of medical or industrial importance. This organism has a NADP-specific glutamate dehydrogenase (NADP-GDH) nuclear-gene encoding a precursor mRNA that appears to be alternatively spliced to yield mRNAs differing in size and encoding enzyme subunits with differing affinities for ammonium. The promoter of this gene may be useful to drive the expression of heterologous genes. The transcription initiation site of the NADP-GDH gene was identified. This site delineates the 3′-border of the promoter region, and 1285 bp upstream from this site have been sequenced. To identify the promoter 5′-border by deletion analysis, this region (coupled to a reporter gene in a plasmid vector) was to be introduced by electroporation intoC. sorokiniana protoplasts. Cells were treated with a mixture of hydrolytic enzymes; however, non-hydrolyzable component(s) in the cell wall inhibited protoplast formation. The cell wall was subsequently shown to contain acetolysis-resistant component(s) identified as sporopollenin-like in other algae. Since sporopollenin was reported earlier to be a polymer of carotenoids/carotenoid-esters, the cells were cultured in the presence of norflurazon, an inhibitor of carotenoid biosynthesis. Whereas synthesis of total carotenoids was inhibited by 75%, synthesis of the acetolysis-resistant component(s) in the cell wall was not inhibited. In addition to the above studies, a revised model for the regulation of expression of theC. sorokiniana NADP-GDH gene is presented.
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  • 2
    ISSN: 1573-5028
    Keywords: alternative splicing ; Chlorella sorokiniana ; chloroplastic ; glutamate dehydrogenase ; isozymes ; precursor mRNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chlorella sorokiniana has seven ammonium-inducible, chloroplastic NADP-specific glutamate dehydrogenase (NADP-GDH) isozymes composed of varying ratios of α- and β-subunits. Southern blot and allele-specific PCR analyses indicate that the C. sorokiniana genome possesses a single 7178 bp nuclear NADP-GDH gene. cDNA cloning and sequencing, 5′-RACE-PCR analysis, and RNase protection analysis identified two NADP-GDH mRNAs that are identical with the exception of a 42 nt sequence located within the 5′-coding region of the longer mRNA. The 42 nt sequence, termed an auxon because it serves as an exon or intron, appears to undergo alternative splicing from the precursor mRNA by a process that is regulated by both nutritional and environmental signals. Depending upon whether the auxon is included or excluded in a mature mRNA, the gene can be considered to consist of 22 or 23 exons, respectively. The 2074 and 2116 nt mRNAs encode precursor proteins of 56350 and 57850 Da, respectively. The N-termini of the purified mature α- and β-subunits were sequenced, identifying full-length subunits of 53501 and 52342 Da, respectively. The sequences of the subunits are identical except for an 11 amino acid extension at the N-terminus of the α-subunit. The α-subunit has an additional α-helical domain at its N-terminus compared with the β-subunit. By correlating the abundances of the two mRNAs with the levels (and relative turnover rates) of the α- and β-subunit antigens during induction in Chlorella, the larger mRNA is proposed to encode the larger subunit.
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  • 3
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The levels of free-, peptide-, and protein-amino acids were measured during the synchronous growth and division cycle of a thermophilic strain of Chlorella pyrenoidosa. Most of the protein amino acids exhibited little periodism (as % of total cellular-N); however, the free- and peptide-amino acids showed a variety of dramatic changes in level during the cell cycle.Fractionation of the acid-soluble peptides by Sephadex gel-filtration showed that an average of only 2.8% of the peptide amino acids were associated with peptides of high molecular weight (〉 5000), while approximately 75% of the peptide amino acids were components of low molecular weight peptides (〈 700). The low molecular weight peptides were predominately made up of relatively few amino acids (i.e., alanine, glutamate, lysine, glycine and arginine accounted for approximately 92% of the low molecular weight peptide amino acids).Several experiments revealed that nucleotide-peptides do not contribute significantly to the pool of acid-soluble peptides during the cell cycle of this organism.
    Additional Material: 7 Ill.
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  • 4
    ISSN: 0095-9898
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Efferent spikes were recorded from the nerves supplying the papilla amphibiorum, ampullae, and lateral-line neuromasts of the mudpuppy (Necturus maculosus). Increased efferent activity was associated with rotatory, vibratory, and tactile stimulation and gill movements. In a single experiment it was possible to record efferents from the nerve to the papilla basilaris of a leopard frog (Rana pipiens). The function of acoustico-lateralis efferents is not restricted to or closely associated with a single habit, habitat, phylogenetic group, or acoustico lateralis receptor. It seems likely that all acoustico-lateralis receptors in all vertebrates receive efferent input.
    Additional Material: 2 Ill.
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  • 5
    ISSN: 0095-9898
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Additional Material: 5 Ill.
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  • 6
    Publication Date: 2013-08-31
    Description: Calculating the effects of impacts leading to global catastrophes requires knowledge of the impact process at very large size scales. This information cannot be obtained directly but must be inferred from subscale physical simulations, numerical simulations, and scaling laws. Schmidt and Holsapple presented scaling laws based upon laboratory-scale impact experiments performed on a centrifuge (Schmidt, 1980 and Schmidt and Holsapple, 1980). These experiments were used to develop scaling laws which were among the first to include gravity dependence associated with increasing event size. At that time using the results of experiments in dry sand and in water to provide bounds on crater size, they recognized that more precise bounds on large-body impact crater formation could be obtained with additional centrifuge experiments conducted in other geological media. In that previous work, simple power-law formulae were developed to relate final crater diameter to impactor size and velocity. In addition, Schmidt (1980) and Holsapple and Schmidt (1982) recognized that the energy scaling exponent is not a universal constant but depends upon the target media. Recently, Holsapple and Schmidt (1987) includes results for non-porous materials and provides a basis for estimating crater formation kinematics and final crater size. A revised set of scaling relationships for all crater parameters of interest are presented. These include results for various target media and include the kinematics of formation. Particular attention is given to possible limits brought about by very large impactors.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., Global Catastrophes in Earth History: An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality; p 162-163
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  • 7
    Publication Date: 2013-08-31
    Description: This research is a continuation of an ongoing program whose objective is to perform experiments and to develop scaling relationships for large body impacts onto planetary surfaces. The development of the centrifuge technique has been pioneered by the present investigator and is used to provide experimental data for actual target materials of interest. With both powder and gas guns mounted on a rotor arm, it is possible to match various dimensionless similarity parameters, which have been shown to govern the behavior of large scale impacts. Current work is directed toward the determination of scaling estimates for nonporous targets. The results are presented in summary form.
    Keywords: GEOPHYSICS
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 396-398
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  • 8
    Publication Date: 2013-08-31
    Description: A geotechnical centrifuge was used to investigate large body impacts onto planetary surfaces. At elevated gravity, it is possible to match various dimensionless similarity parameters which were shown to govern large scale impacts. Observations of crater growth and target flow fields have provided detailed and critical tests of a complete and unified scaling theory for impact cratering. Scaling estimates were determined for nonporous targets. Scaling estimates for large scale cratering in rock proposed previously by others have assumed that the crater radius is proportional to powers of the impactor energy and gravity, with no additional dependence on impact velocity. The size scaling laws determined from ongoing centrifuge experiments differ from earlier ones in three respects. First, a distinct dependence of impact velocity is recognized, even for constant impactor energy. Second, the present energy exponent for low porosity targets, like competent rock, is lower than earlier estimates. Third, the gravity exponent is recognized here as being related to both the energy and the velocity exponents.
    Keywords: GEOPHYSICS
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 391
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