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  • 1
    Electronic Resource
    Electronic Resource
    Arabinofuranosyl nucleosides induce common fragile sites (1988)
    Springer
    Human genetics 〈Berlin〉 79 (1988), S. 157-162 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The capacities for fragile site induction of three inhibitors of semiconservative DNA synthesis and DNA repair synthesis, aphidicolin, arabinofuranosyl cytosine, and arabinofuranosyl adenosine were compared. Aphidicolin is known to induce type 4 fragile sites, the largest recognized group of common fragile sites. Although the modes of action of these inhibitors vary, both arabinofuranosyl analogs induce type 4 aphidicolin-sensitive fragile sites. An analysis of variance demonstrates that the three inhibitors are not equally capable of inducing significant breakage (P〈0.01) at all type 4 fragile sites. Induction of type 4 fragile sites appears to be a general consequence of inhibition of DNA polymerization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280556
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  • 2
    Electronic Resource
    Electronic Resource
    Electrophoretic karyotype of Cercospora kikuchii (1995)
    Springer
    Current genetics 27 (1995), S. 290-292 
    Details
    ISSN: 1432-0983
    Keywords: Cercospora kikuchii ; Electrophoretic karyotype ; Genome size Pulsed-field gel electrophoresis Cercosporin biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Classical genetic analyses are not possible with the phytopathogenic fungus Cercospora kikuchii since no sexual stage has been identified. To facilitate gene mapping and to develop an understanding of the genome organization of C. kikuchii, an electrophoretic karyotype has been obtained using contour-clamped homogeneous electric field gel electrophoresis (CHEF). Eight chromosomes, two of which migrate as a doublet, have been separated into seven bands ranging from 2.0 to 5.5 Mb. Using this determination of chromosome number and size, the total genome size of C. kikuchii is estimated to be 28.4 Mb. In addition, genes encoding tubulin, ribosomal DNA, and four previously isolated light-enhanced cDNAs from C. kikuchii were assigned to chromosomes by Southern-hybridization analysis of CHEF blots.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326163
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  • 3
    Electronic Resource
    Electronic Resource
    Selective DNA amplification regulates transcript levels in plant mitochondria (1995)
    Springer
    Current genetics 28 (1995), S. 113-121 
    Details
    ISSN: 1432-0983
    Keywords: Transcription ; Plant ; Mitochondria ; Copy number ; Gene regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Most plant mitochondrial genomes exist as subgenomic-size fragments apparently due to recombination between repetitive sequences. This leads to the possibility that independently replicating subgenomic domains could result in mitochondrial gene copy number variation. We show, through Southern-blot analysis of both restricted and intact mtDNA, that there are gene-specific copy number differences in the monocot Zea mays. Comparison of two different maize genotypes, B37(N) and B37(T), a cytoplasmic male-sterile strain, reveal fewer gene copy number differences for B37(T) than for B37(N). In contrast to maize, significant gene copy number differences are not detected in the dicot Brassica hirta. We also demonstrate that mitochondrial transcriptional rates in both species are apparently dependent on gene copy number since relative rates determined by run-on analysis are proportional to relative gene copy numbers. Thus a direct relationship exists between plant mitochondrial gene copy number and transcriptional rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00315776
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  • 4
    Electronic Resource
    Electronic Resource
    Repetitive mixing events and holocene pyroclastic activity at Pico de Orizaba and Popocatepetl (Mexico) (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 735-748 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Holocene volcanic activity which built up the present terminal cones of Pico de Orizaba and Popocatepetl in eastern Mexico, was characterized by repeated pyroclastic Saint-Vincent type eruptions. Radiocarbon data show that these paroxysmal events occurred at more or less regular intervals, and were followed by moderate activity producing ash and pumice falls and andesitic lava flows from the summit craters. Typical ash and scoria pyroclastic flows exhibit a heterogeneous composition given by the interaction of a dacitic component with a more basic andesitic one. Scoria bombs are characterized by banded to emulsified textures, mineralogical desequilibrium assemblages and linear chemical variations on element-element plots as exemplified by the Loma Grande flow at Pico. Periodic replenishments of the magmatic reservoir could be the major phenomenon that started mixing and consequently triggered the pyroclastic eruptions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952341
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  • 5
    Electronic Resource
    Electronic Resource
    Transcription in maize mitochondria: effects of tissue and mitochondrial genotype (1992)
    Springer
    Current genetics 22 (1992), S. 235-242 
    Details
    ISSN: 1432-0983
    Keywords: Maize mitochondria ; Transcription rate ; Maize tissue ; Mitochondrial genotype
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mitochondrial run-on assays were used to determine transcriptional rates for nine B37(N) maize mitochondrial genes. Quantiation by radiographic imaging detected a 15-fold range in transcriptional rates; the order of apparent promoter strength was rps12〉rrn26〉atp6〉rrn18〉cox2〉atpα〉atp9〉cox3〉 cob. By probing single-stranded DNAs of both polarities with the run-on-products we showed that gene-specific antisense transcription did not occur. We also tested whether relative transcriptional rates were dependent on either the mitochondrial genotype or the tissue from which the mitochondria were isolated. Although tissue-specific differences in transcriptional rates were not detected, significant variation in apparent promoter strength for at least one gene, rps12, was dependent on the cytoplasmic genotype; rps12 had a five-fold reduced transcriptional rate in B37(T), the Texas male cytoplasmic strain of maize. Pulse-chase experiments suggested that differential transcript stability was not a major determinant of steady state mitochondrial RNA levels. These results indicate not only that promoter strength is an important component of the regulation of transcript levels in maize mitochondria, but also that the strength of a specific gene promoter can be dependent on the cytoplasmic genotype. Finally, the high transcriptional rate of both ribosomal RNA genes and the one mitochondrially encoded ribosomal protein gene studied suggests coordinate transcriptional regulation of both RNA and protein components of the mitochondrial ribosome.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00351731
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  • 6
    Electronic Resource
    Electronic Resource
    Stool Water Content and Colonic Drug Absorption: Contrasting Effects of Lactulose and Codeine (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 1254-1259 
    Details
    ISSN: 1573-904X
    Keywords: colon ; absorption ; EDTA ; quinine ; lactulose ; codeine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. By varying stool water content using lactulose and codeine, we investigated the influence of luminal water content on the absorption of quinine, a transcellular probe, and 5lCr-EDTA, a paracellular probe, from the distal gut. Methods. Sixteen volunteers entered a three-way cross-over trial in which absorption of probe markers from a timed-release delivery system was determined following treatment with lactulose 20 mls tds (increasing water content), or codeine 30 gms qds (decreasing water content), and compared with control untreated values. Stool water content was assessed by freeze drying stool samples. Site of release was determined by gamma scintigraphy, and absorption was measured by plasma levels and urinary recovery of the marker probes. Results. Lactulose accelerated ascending colon transit (3.7 ± 0.8 vs 4.5 ± 1.4 hrs, p 〈 0.05), increased stool water content (75 ± 2 vs 71 ± 2%, p 〈 0.01), caused greater dispersion of released material (dispersion score 3.4 ± 0.3 vs 1.8 ± 0.2, p 〈 0.01), and enhanced absorption of the transcellular probe quinine (4.66 ± 0.78 vs 3.02 ± 0.63%, p 〈 0.05) compared to control. Conversely codeine slowed ascending colon transit (8.9 ± 1.8 hrs), reduced stool water content (61 ± 2 vs 71.2%, p 〈 0.05), and tended to diminish absorption (2.60 ± 0.77 vs 3.02 ± 0.63%, p = 0.20). Within the ascending colon specifically, there was a significant trend for treatments increasing luminal water content to enhance quinine absorption (medians: codeine = 1.2%, [n = 8] 〈 control = 2.3%, [n = 5] 〈 lactulose = 3.2%, [n = 7], p 〈 0.01). Delivery site also had an important influence on absorption, with more distal release resulting in less absorption in the control arm (medians: small intestine = 4.4% [n = 5] 〉 ascending colon = 2.3% [n = 5] 〉 transverse colon = 1.5% [n = 6], p 〈 0.005). Conclusions. Lactulose accelerates transit, increases stool water content, and enhances drug absorption from the distal gut whilst codeine slows transit, decreases stool water content, and tends to diminish absorption, compared to controls. We conclude that water content may be an important determinant in colonic drug absorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1014805815499
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  • 7
    Electronic Resource
    Electronic Resource
    Echo-Planar Magnetic Resonance Imaging to Assess Water Volume in the Distal Small Bowel (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 1134-1139 
    Details
    ISSN: 1573-904X
    Keywords: mannitol ; small intestinal transit ; echo-planar magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Assessment of fluid volumes and flow through the small intestine has in the past only been possible by means of invasive intubation studies on human volunteers. Intubation very likely disturbs gut motility and stimulates secretion. Methods. The aim of this study was to utilise the new technique of echo-planar magnetic resonance imaging in order to non-invasively visualise the changing volume of water in the small intestinal lumen. 200mls of test solution was ingested and water volume assessed using a multi-slice scanning technique on 3 separate days. The solutions were pure water, pure water plus 2.264 or l0g of mannitol. These were taken on separate days by 8 healthy male volunteers. Regions of interest were constructed in the area of the lower pelvis excluding retroperitoneal structures. Results. The water content of the lower small intestine did not change significantly over the 4 hours after the control solution. By contrast after both mannitol solutions there was an increase in the amount of water in the distal intestine as assessed by the area under the curve of the volume time profile (Control 51 ml.h (SD ±47); mannitol 2.264g/200ml 72ml.h (SD ±57); 10g/200ml mannitol 115ml.h (SD ±56)). Page's L Trend test showed that the trend for the volume to increase with increasing mannitol concentration to be statistically significant at the 1% level (L= 108). Conclusions. The study highlights the potential of echo-planar magnetic resonance imaging to visualise changes in gastrointestinal physiology in a non-invasive manner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016251624220
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  • 8
    Electronic Resource
    Electronic Resource
    Regional Differences in Quinine Absorption from the Undisturbed Human Colon Assessed Using a Timed Release Delivery System (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 1087-1092 
    Details
    ISSN: 1573-904X
    Keywords: transcellular ; paracellular ; absorption ; gastrointestinal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To investigate the regional absorption characteristics of the distal gut using two markers of permeability, quinine (a transcellular probe) and 51CrEDTA (a paracellular probe). Methods. The permeability markers were delivered to the undisturbed gastrointestinal tract in 39 healthy volunteers using an oral timed-release delivery vehicle which allowed pulsed release within a particular site of the gut. Site of release was identified using gamma scintigraphy. Absorption of quinine and 5lCrEDTA was assessed by measuring the percent excretion in the urine using HPLC and gamma counting respectively. Serial plasma samples allowed time-concentration curves for quinine to be plotted. Results. There was a significant trend for diminished absorption with more distal delivery of the transcellular probe, quinine, which was: 6.26 ± 0.87% (small intestine, n = 10); 4.65 ± 0.93% (ascending colon, n = 16); and 2.59 ± 0.52% (transverse colon, n = 10) of the ingested dose excreted respectively (p 〈 0.001). No such gradient was seen with the paracellular marker, 5lCrEDTA. Conclusions. These results suggest that delayed release formuations should aim for release in the distal small bowel and proximal colon if absorption is to be miximised. Absorption by the transcellular route diminishes in the more distal colon, a fact which has implications for delayed or sustained release formulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018948102778
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  • 9
    Electronic Resource
    Electronic Resource
    Late Holocene eruptive activity at Nevado Cayambe Volcano, Ecuador (1998)
    Springer
    Bulletin of volcanology 59 (1998), S. 451-459 
    Details
    ISSN: 1432-0819
    Keywords: Key words Tephrochronology ; Pyroclastic flow ; Holocene ; Cayambe Volcano ; Ecuador
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Four Late Holocene pyroclastic units composed of block and ash flows, surges, ashfalls of silicic andesite and dacite composition, and associated lahar deposits represent the recent products emitted by domes on the upper part of Nevado Cayambe, a large ice-capped volcano 60 km northeast of Quito. These units are correlated stratigraphically with fallout deposits (ash and lapilli) exposed in a peat bog. Based on 14C dating of the peat and charcoal, the following ages were obtained: ∼910 years BP for the oldest unit, 680–650 years BP for the second, and 400–360 years BP for the two youngest units. Moreover, the detailed tephrochronology observed in the peat bog and in other sections implies at least 21 volcanic events during the last 4000 years, comprising three principal eruptive phases of activity that are ∼300, 800, and 900 years in duration and separated by repose intervals of 600–1000 years. The last phase, to which the four pyroclastic units belong, has probably not ended, as suggested by an eruption in 1785–1786. Thus, Cayambe, previously thought to have been dormant for a long time, should be considered active and potentially dangerous to the nearby population of the Interandean Valley.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450050203
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  • 10
    Electronic Resource
    Electronic Resource
    Le Volcan Popocatepetl (Mexique): structure, evolution pétrologique et risques (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 1-23 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Volcan Popocatepetl, which lies 70 km southeast of Mexico City, is one of the most famous andesite composite volcanoes in the world. With 5,450 m of elevation, it is the second highest peak of Mexico. Located 320 km north of the Middle America Trench, at the centre of the Mexican Volcanic Belt, Volcano Popocatepetl forms the southern active part of a northsouth volcanic complex, the northern part consisting of the eroded Volcano Iztaccihuatl. Since its earliest reported eruption in 1519, Volcano Popocatepetl has had a continuous fumarolic activity in its crater, and in frequent small eruptions (1720, 1802–1804, 1920). In contrast with this light activity, C14 data indicate pre-historical cycles of intense volcanism with paroxysmal pyroclastic eruptions (ash and pumice-flows) alternating with effusive phases and plinian air-fall deposits. The results of a volcanological study and the petrological characteristics of the main volcanic units show that Volcano Popocatepetl is composed of a primitive composite-volcano on which a recent summit cone is superimposed. It has been built during 2 very dissimilar volcanic periods linked by a transitional phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01960537
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