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  • 1
    Electronic Resource
    Electronic Resource
    Enhanced Evolvability in Immunoglobulin V Genes Under Somatic Hypermutation (1999)
    Springer
    Journal of molecular evolution 49 (1999), S. 23-26 
    Details
    ISSN: 1432-1432
    Keywords: Key words: Genome evolution — Adaptability — Somatic hypermutation — Affinity maturation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Darwinian theory requires that mutations be produced in a nonanticipatory manner; it is nonetheless consistent to suggest that mutations that have repeatedly led to nonviable phenotypes would be introduced less frequently than others—if under appropriate genetic control. Immunoglobulins produced during infection acquire point mutations that are subsequently selected for improved binding to the eliciting antigen. We and others have speculated that an enhancement of mutability in the complementarity-determining regions (CDR; where mutations have a greater chance of being advantageous) and/or decrement of mutability in the framework regions (FR; where mutations are more likely to be lethal) may be accomplished by differential codon usage in concert with the known sequence specificity of the hypermutation mechanism. We have examined 115 nonproductively rearranged human Ig sequences. The mutation patterns in these unexpressed genes are unselected and therefore directly reflect inherent mutation biases. Using a χ2 test, we have shown that the number of mutations in the CDRs is significantly higher than the number of mutations found in the FRs, providing direct evidence for the hypothesis that mutations are preferentially targeted into the CDRs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00006530
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  • 2
    Electronic Resource
    Electronic Resource
    15N CP/MAS NMR as an instrument in structure investigations of organosilicon polymers (1999)
    Springer
    Fresenius' journal of analytical chemistry 363 (1999), S. 185-188 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 15N solid state NMR without enrichment is rarely used because of the low sensitivity and low natural abundance of this nucleus. As demonstrated on different nitrogen-containing polysilanes and polysilazanes, it can be shown that with the CP/MAS technique spectra can be obtained in good quality and within acceptable measuring time. Three main different nitrogen sites – NSi3, NSi2H and NSiH2– can be observed as well as changes in the intensities of these sites with reaction and tempering conditions. Thus the spectra give valuable additional information for a better understanding of the structures and their changes within the investigated systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160051168
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  • 3
    Electronic Resource
    Electronic Resource
    Genetic relationships among Stylosanthes species revealed by RFLP and STS analyses (1999)
    Springer
    Theoretical and applied genetics 99 (1999), S. 1179-1186 
    Details
    ISSN: 1432-2242
    Keywords: Key words Stylosanthes ; DNA markers ; Genetic relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Genetic relationships between 6 unclassified taxa and 24 known species of the genus Stylosanthes were investigated by RFLP and STS analyses. This allowed the diploid taxa used in this study to be classified into nine basal (genome) groups. Representative species in these groups included ’S. seabrana’/S. hamata (Group A), S. viscosa (Group B), S. humilis (Group C), S. macrocephala/S. bracteata (Group D), S. pilosa (Group E), S. leiocarpa (Group F), S. guianensis (Group G), S. tomentosa (Group H) and S. calcicola (Group I). Polyploid taxa used were grouped into five classes based on their putative genomic structures. These are AABB for S. scabra, S. aff. scabra, S. sericeiceps, S. aff. hamata and S. tuberculata; AACC for S. mexicana, S. subsericea, S. sundaica and S. sp.A; DDEE for S. capitata; AAFF for S. sympodialis; and AABBXX for S. erecta, with XX representing an unknown genome. Of the 6 unclassified taxa, three were diploids and 3 tetraploids. Of the 3 diploids, the genome of S. sp. was markedly distinct from those of all other diploids analysed in this study, with that of S. leiocarpa being the closest. The genome of S. sp.B was similar to that of S. humilis, with an average dissimilarity value of 15% between them. The genome of S. aff. viscosa was very similar to that of S. viscosa. Genetic variation between these 2 taxa was not larger than that within each of the 2 taxa. Of the 3 tetraploids, the genomic structure of S. sp.A was similar to those of S. mexicana, S. sundaica and S. subsericea, and the genomic structures of S. aff. scabra and S. aff. hamata were similar to those of S. scabra and S. sericeiceps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220051322
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of reforestation methods on genetic diversity of lodgepole pine: an assessment using microsatellite and randomly amplified polymorphic DNA markers (1999)
    Springer
    Theoretical and applied genetics 98 (1999), S. 793-801 
    Details
    ISSN: 1432-2242
    Keywords: Key words Pinus contorta ; Silviculture ; Reforestation ; Gene conservation ; RAPD ; SSR ; DNA analyses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We examined the effects of different methods of forest regeneration on the genetic diversity of lodgepole pine (Pinus contorta var ‘latifolia’) using two different DNA-based molecular markers [randomly amplified polymorphic DNA (RAPDs) and microsatellites or simple sequence repeats (SSRs)]. Genetic diversity was estimated for 30 individuals in each of four populations for the following three stand types: (1) mature lodgepole pine (〉100 years); (2) 20- to 30-year-old harvested stands left for natural regeneration; (3) 20- to 30-year-old planted stands (4 stands of each type); and one group of 30 operationally produced seedlings. There was no significant effect of stand type on expected heterozygosity, although allelic richness and diversity were much higher for SSRs than for RAPDs. Expected heterozygosity ranged from 0.39 to 0.47 based on RAPDs and from 0.67 to 0.77 based on SSRs. The number of alleles per locus for SSRs ranged from 3 to 34 (mean 21.0), and there was a significant relationship between sequence repeat length and the number of alleles at a locus. Both marker types showed that over 94% of the variation was contained within the populations and that the naturally regenerated stands sampled had lower (not significant) expected heterozygosity than the planted or unharvested stands. The group of seedlings (assessed by RAPDs only) had expected heterozygosity and allele frequencies similar to those of the unharvested stands. Genetic distance measures were higher than obtained previously in the species using isozyme markers. There was no correlation between the two marker types for pair-wise genetic distances based on populations analyzed by both methods. Pair-wise genetic distance measures and an ordination of allele frequencies for both marker types showed little effect of geographic location or stand type on genetic similarity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220051136
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  • 5
    Electronic Resource
    Electronic Resource
    Residue Management of Perennial Ryegrass and Tall Fescue Seed Crops (1999)
    Springer
    Semigroup forum 91 (1999), S. 671-675 
    Details
    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Lolium perenne L. cv. Regal and Pleasure) and tall fescue (Festuca arundinacea Schreb. cv. Martin and Rebel II). Seed yield components were measured to identify the components through which treatments affect yield. Treatments did not affect seed yield of Regal perennial ryegrass and Martin tall fescue in any crop year. Third-crop seed yield of Pleasure perennial ryegrass was 15% higher for the open-burn than for the flail-chop treatment; fourth-crop seed yield was 12% higher for the open-burn treatment than for either flail-chop or propane-burn. Across years, seed yields of Rebel II tall fescue for propane-burn and open-burn treatments were 8 and 12% greater, respectively, than for flail-chop. Where seed yields were affected, differences among treatments were through changes in seed number per unit area (seeds m-2), but seed weight was relatively stable. Treatments did not affect the number of fertile tillers in any cultivar. Variations in seed number were apparently due to treatment effects on the number of seeds set per tiller. We conclude that the need for postharvest residue burning in perennial ryegrass and tall fescue is cultivar specific. Mechanical residue removal is apparently as effective as open-field burning for maintaining high seed yields in some cultivars of these grasses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/
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  • 6
    Electronic Resource
    Electronic Resource
    Selenium Bioaccumulation by the Water Boatman Trichocorixa reticulata (Guerin-Meneville) (1999)
    Springer
    Archives of environmental contamination and toxicology 36 (1999), S. 295-300 
    Details
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract. The input of selenium from subsurface agricultural drainage into surface water systems can result in the accumulation of toxic concentrations of selenium in aquatic food chains. Elevated selenium concentrations in aquatic systems is a significant environmental problem in many areas of the United States. A laboratory investigation was conducted to determine the dominant route of selenium bioaccumulation by the corixid Trichocorixa reticulata, an important food chain organism. The roles of waterborne and foodborne exposure in selenium bioaccumulation were examined using 48-h bioassays. Waterborne selenium concentrations ranged from 0 to 1,000 μg Se/L as selenate. A mixture of two species of blue-green algae cultured in media with selenium concentrations ranging from 0 to 1,000 μg Se/L as selenate was used as a corixid diet in the foodborne treatments. Corixids exposed to waterborne selenate did not accumulate selenium above control concentrations. Corixids fed algae exposed to ≥100 μg Se/L as selenate had significantly higher selenium concentrations than control organisms. These data suggest that corixids may be effectively isolated from the water and selenium accumulation is solely through dietary exposure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002449900474
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  • 7
    Electronic Resource
    Electronic Resource
    Hyperactivation of Mitogen-Activated Protein Kinase Increases Phospho-Tau Immunoreactivity Within Human Neuroblastoma: Additive and Synergistic Influence of Alteration of Additional Kinase Activities (1999)
    Springer
    Cellular and molecular neurobiology 19 (1999), S. 249-260 
    Details
    ISSN: 1573-6830
    Keywords: MAP kinase ; tau ; protein kinase C ; wortmannin ; PD98059 ; neuroblastoma ; Alzheimer's disease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mitogen-activated protein (MAP) kinase phosphorylates tau in cell-free analyses, but whether or not it does so within intact cells remains controversial. In the present study, microinjection of MAP kinase into SH-SY-5Y human neuroblastoma cells increased tau immunoreactivity toward the phosphodependent antibodies PHF-1 and AT-8. In contrast, treatment with a specific inhibitor of MAP kinase (PD98059) did not diminish “basal” levels of these immunoreactivities in otherwise untreated cells. These findings indicate that hyperactivation of MAP kinase increases phospho-tau levels within cells, despite that MAP kinase apparently does not substantially influence intracellular tau phosphorylation under normal conditions. These findings underscore that results obtained following inhibition of kinase activities do not necessarily provide an indication of the consequences accompanying hyperactivation of that same kinase. Several studies conducted in cell-free systems indicate that exposure of tau to multiple kinases can have synergistic effects on the nature and extent of tau phosphorylation. We therefore examined whether or not such effects could be demonstrated within these cells. Site-specific phospho-tau immunoreactivity was increased in additive and synergistic manners by treatment of injected cells with TPA (which activates PKC), calcium ionophore (which activates calcium-dependent kinases), and wortmannin (which inhibits PIP3 kinase). Alteration in total tau levels was insufficient to account for the full extent of the increase in phospho-tau immunoreactivity. These additional results indicate that multiple kinase activities modulate the influence of MAP kinase on tau within intact cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006981228331
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  • 8
    Electronic Resource
    Electronic Resource
    The Order of Exposure of Tau to Signal Transduction Kinases Alters the Generation of “AD-Like” Phosphoepitopes (1999)
    Springer
    Cellular and molecular neurobiology 19 (1999), S. 223-233 
    Details
    ISSN: 1573-6830
    Keywords: tau ; kinases ; signal transduction ; Alzheimer's disease ; phosphorylation ; paired helical filaments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 1. The individual and sequential influence of protein kinase C (PKC), protein kinase A (PKA) and mitogen-activated protein kinase (MAP kinase) on human brain tau was examined. 2. A range of PKC concentrations generated certain phosphoepitopes common with paired helical filaments. These epitopes were masked by higher PKC concentrations, suggesting the presence of multiple tau phosphorylation sites for which PKC exhibited differing affinities and/or conformational alterations in tau induced by sequential PKC-mediated phosphorylation. 3. Prior phosphorylation by PKC enhanced the nature and extent of AD-like tau antigenicity generated by subsequent incubation with MAP kinase yet inhibited that generated by subsequent incubation with PKA. 4. Dephosphorylation of tau prior to incubation with kinases significantly altered the influence of individual and multiple kinase incubation on tau antigenicity in a site-specific manner, indicating that prior in situ phosphorylation events markedly influenced subsequent cell-free phosphorylation. 5. In addition to considerations of the potential impact of tau phosphorylation by individual kinases, these findings extend previous studies which indicate that tau antigenicity, and, presumably, its behavior in situ, is influenced by the sequential and convergent influences of multiple kinases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006977127422
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  • 9
    Electronic Resource
    Electronic Resource
    Multivariate nonhomogeneous refinement equations (1999)
    Springer
    The journal of Fourier analysis and applications 5 (1999), S. 589-597 
    Details
    ISSN: 1531-5851
    Keywords: 42C15 ; 39B99 ; multivariate ; nonhomogeneous ; refinement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We give necessary and sufficient conditions for the existence and uniqueness of compactly supported distribution solutionsf=(f 1,...,f r)T of nonhomogeneous refinement equations of the form $$f(x) = h(x) + \sum\limits_{\alpha \in A} {c_\alpha f(2x - \alpha )(x \in R^s )} $$ , where h=(h1,...,hr)Tis a compactly supported vector-valued multivariate distribution, A⊂Z+ s has compact support, and the coefficientsc α are real-valued r×r matrices. In particular, we find a finite dimensional matrix B, constructed from the coefficientsc α of the equation (I−B)q=p, where the vectorp depends on h. Our proofs proceed in the time domain and allow us to represent each solution regardless of the spectral radius of P(0):=2−s∑c α , which has been a difficulty in previous investigations of this nature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01257193
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  • 10
    Electronic Resource
    Electronic Resource
    The third leg: Molecular dynamics simulations of lipid binding proteins (1999)
    Springer
    Molecular and cellular biochemistry 192 (1999), S. 143-156 
    Details
    ISSN: 1573-4919
    Keywords: molecular dynamics ; LBP ; FABP ; structure-function ; protein-lipid interactions ; rational drug design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Molecular dynamics computer simulations can provide a third leg which balances the contributions of both structural biology and binding studies performed on the lipid binding protein family. In this context, these calculations help to establish a dialogue between all three communities, by relating experimental observables with details of structure. Working towards this connection is important, since experience has shown the difficulty of inferring thermodynamic properties from a single static conformation. The challenge is exemplified by ongoing attempts to interpret the impact of mutagenesis on structure and function (i.e. binding). A detailed atomic-level understanding of this system could be achieved with the support of all three legs, paving the way towards rational design of proteins with novel specificities. This paper provides an outline of the connections possible between experiment and theory concerning lipid binding proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006818203334
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