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201.
Georg Greiner Lydia Seyfarth Wolfgang Poppitz Raiker Witter Ullrich Sternberg Siegmund Reissmann 《Letters in Peptide Science》2000,7(3):133-141
Seven pseudotripeptides with the common structure Bz-His-[CO-N(CH2)n-X]Gly-His-NH2 were synthesized on the solid phase using the Fmoc-strategy, trityl protection for both His residues and Boc- or -OBut-protection for N-aminoalkyl- and N-carboxyalkyl residues, respectively. Functionalized N-alkyl glycyl peptides were formed on the solid phase by amination of a bromoacetyl dipeptide. All seven pseudotripeptides are able to form chelate complexes with the metal ions Zn2+, Ni2+, Cu2+ and Co2+. The existence of monomeric 1:1 complexes for these pseudopeptides was calculated from the MW estimated by MALDI-MS and from the isotope distribution pattern estimated by ESI. 相似文献
202.
In C. elegans, the descendants of the 1 degrees vulval precursor cell (VPC) establish a fixed spatial pattern of two different cell fates: E-F-F-E. The two inner granddaughters attach to the somatic gonadal anchor cell (AC) and generate four vulF cells, while the two outer granddaughters produce four vulE progeny. zmp-1::GFP, a molecular marker that distinguishes these two fates, is expressed in vulE cells, but not vulF cells. We demonstrate that a short-range AC signal is required to ensure that the pattern of vulE and vulF fates is properly established. In addition, signaling between the inner and outer 1 degrees VPC descendants, as well as intrinsic polarity of the 1 degrees VPC daughters, is involved in the asymmetric divisions of the 1 degrees VPC daughters and the proper orientation of the outcome. Finally, we provide evidence that RAS signaling is used during this new AC signaling event, while the Wnt receptor LIN-17 appears to mediate signaling between the inner and outer 1 degrees VPC descendants. 相似文献
203.
We investigate the extent to which the conformational fluctuations of proteins in solution reflect the conformational changes that they undergo when they form binary protein-protein complexes. To do this, we study a set of 41 proteins that form such complexes and whose three-dimensional structures are known, both bound in the complex and unbound. We carry out molecular dynamics simulations of each protein, starting from the unbound structure, and analyze the resulting conformational fluctuations in trajectories of 5 ns in length, comparing with the structure in the complex. It is found that fluctuations take some parts of the molecules into regions of conformational space close to the bound state (or give information about it), but at no point in the simulation does each protein as whole sample the complete bound state. Subsequent use of conformations from a clustered MD ensemble in rigid-body docking is nevertheless partially successful when compared to docking the unbound conformations, as long as the unbound conformations are themselves included with the MD conformations and the whole globally rescored. For one key example where sub-domain motion is present, a ribonuclease inhibitor, principal components analysis of the MD was applied and was also able to produce conformations for docking that gave enhanced results compared to the unbound. The most significant finding is that core interface residues show a tendency to be less mobile (by size of fluctuation or entropy) than the rest of the surface even when the other binding partner is absent, and conversely the peripheral interface residues are more mobile. This surprising result, consistent across up to 40 of the 41 proteins, suggests different roles for these regions in protein recognition and binding, and suggests ways that docking algorithms could be improved by treating these regions differently in the docking process. 相似文献
204.
Yaghmaie F Saeed O Garan SA Freitag W Timiras PS Sternberg H 《Neuro endocrinology letters》2005,26(3):197-203
Life-long calorie restriction (CR) remains the most robust and reliable means of extending life span in mammals. Among the several theories to explain CR actions, one variant of the neuroendocrine theories of aging postulates that changing hypothalamic sensitivity to endocrine feedback is the clock that times phenotypic change over the life span. If the feedback sensitivity hypothesis is correct, CR animals should display a significantly different pattern of hormone-sensitive cell density and distribution in the hypothalamus. Of the many endocrine signal receptors that may be involved in maintaining hypothalamic feedback sensitivity, our study has selected to begin mapping those for estrogen (E). Altered hypothalamic sensitivity to E is known to schedule reproductive maturation and influence reproductive senescence. Taking estrogen receptor-alpha (ERalpha) immunoreactivity as an index of sensitivity to E, we counted ERalpha immunoreactive and non-immunoreactive cells in the pre-optic hypothalamus of young (6 weeks), ad-libitum (Old-AL) fed old (22 months), and calorie restricted (Old-CR) old (22 months) female B6D2F1 mice. An automated imaging microscopy system (AIMS) was used to generate cell counts for each sampled section of pre-optic hypothalamus. Results show a 38% reduction in ERalpha immunoreactive cells and an 18% reduction in total cell numbers in AL-old mice in comparison to young mice. However, CR mice only show a 19% reduction in ERalpha immunoreactive cells and a 13% reduction in total cell numbers in comparison to young mice. This indicates CR prevents age-related cell loss and maintains estrogen sensitivity in the pre-optic hypothalamus of old female B6D2F1 mice. 相似文献
205.
206.
Sharon M. L. Ewe Leonel da Silveira Lobo Sternberg 《Trees - Structure and Function》2005,19(2):119-128
Schinus terebinthifolius Raddi (Schinus) is an invasive exotic species widely found in disturbed and native communities of Florida. This species has been shown to displace native species as well as alter community structure and function. The purpose of this study was to determine if the growth and gas exchange patterns of Schinus, under differing salinity conditions, were different from native species. Two native upland glycophytic species (Rapanea punctata and Randia aculeata) and two native mangrove species (Rhizophora mangle and Laguncularia racemosa) were compared with the exotic. Overall, the exotics morphologic changes and gas exchange patterns were most similar to R. mangle. Across treatments, increasing salinity decreased relative growth rate (RGR), leaf area ratio (LAR) and specific leaf area (SLA) but did not affect root/shoot ratios (R:S). Allocation patterns were however significantly different among species. The largest proportion of Schinus biomass was allocated to stems (47%), resulting in plants that were generally taller than the other species. Schinus also had the highest SLA and largest total leaf area of all species. This meant that the exotic, which was taller and had thinner leaves, was potentially able to maintain photosynthetic area comparable to native species. Schinus response patterns show that this exotic exhibits some physiological tolerance for saline conditions. Coupled with its biomass allocation patterns (more stem biomass and large area of thin leaves), the growth traits of this exotic potentially provide this species an advantage over native plants in terms of light acquisition in a brackish forested ecosystem. 相似文献
207.
Why repetitive DNA is essential to genome function 总被引:1,自引:0,他引:1
Shapiro JA von Sternberg R 《Biological reviews of the Cambridge Philosophical Society》2005,80(2):227-250
There are clear theoretical reasons and many well-documented examples which show that repetitive, DNA is essential for genome function. Generic repeated signals in the DNA are necessary to format expression of unique coding sequence files and to organise additional functions essential for genome replication and accurate transmission to progeny cells. Repetitive DNA sequence elements are also fundamental to the cooperative molecular interactions forming nucleoprotein complexes. Here, we review the surprising abundance of repetitive DNA in many genomes, describe its structural diversity, and discuss dozens of cases where the functional importance of repetitive elements has been studied in molecular detail. In particular, the fact that repeat elements serve either as initiators or boundaries for heterochromatin domains and provide a significant fraction of scaffolding/matrix attachment regions (S/MARs) suggests that the repetitive component of the genome plays a major architectonic role in higher order physical structuring. Employing an information science model, the 'functionalist' perspective on repetitive DNA leads to new ways of thinking about the systemic organisation of cellular genomes and provides several novel possibilities involving repeat elements in evolutionarily significant genome reorganisation. These ideas may facilitate the interpretation of comparisons between sequenced genomes, where the repetitive DNA component is often greater than the coding sequence component. 相似文献
208.
van Swinderen B Metz LB Shebester LD Mendel JE Sternberg PW Crowder CM 《Genetics》2001,158(2):643-655
To identify genes controlling volatile anesthetic (VA) action, we have screened through existing Caenorhabditis elegans mutants and found that strains with a reduction in Go signaling are VA resistant. Loss-of-function mutants of the gene goa-1, which codes for the alpha-subunit of Go, have EC(50)s for the VA isoflurane of 1.7- to 2.4-fold that of wild type. Strains overexpressing egl-10, which codes for an RGS protein negatively regulating goa-1, are also isoflurane resistant. However, sensitivity to halothane, a structurally distinct VA, is differentially affected by Go pathway mutants. The RGS overexpressing strains, a goa-1 missense mutant found to carry a novel mutation near the GTP-binding domain, and eat-16(rf) mutants, which suppress goa-1(gf) mutations, are all halothane resistant; goa-1(null) mutants have wild-type sensitivities. Double mutant strains carrying mutations in both goa-1 and unc-64, which codes for a neuronal syntaxin previously found to regulate VA sensitivity, show that the syntaxin mutant phenotypes depend in part on goa-1 expression. Pharmacological assays using the cholinesterase inhibitor aldicarb suggest that VAs and GOA-1 similarly downregulate cholinergic neurotransmitter release in C. elegans. Thus, the mechanism of action of VAs in C. elegans is regulated by Goalpha, and presynaptic Goalpha-effectors are candidate VA molecular targets. 相似文献
209.
The use of stable isotopes to study ecosystem gas exchange 总被引:24,自引:0,他引:24
Stable isotopes are a powerful research tool in environmental sciences and their use in ecosystem research is increasing.
In this review we introduce and discuss the relevant details underlying the use of carbon and oxygen isotopic compositions
in ecosystem gas exchange research. The current use and potential developments of stable isotope measurements together with
concentration and flux measurements of CO2 and water vapor are emphasized. For these applications it is critical to know the isotopic identity of specific ecosystem
components such as the isotopic composition of CO2, organic matter, liquid water, and water vapor, as well as the associated isotopic fractionations, in the soil-plant- atmosphere
system. Combining stable isotopes and concentration measurements is very effective through the use of ”Keeling plots.” This
approach allows the identification of the isotopic composition and the contribution of ecosystem, or ecosystem components,
to the exchange fluxes with the atmosphere. It also allows the estimation of net ecosystem discrimination and soil disequilibrium
effects. Recent modifications of the Keeling plot approach permit examination of CO2 recycling in ecosystems. Combining stable isotopes with dynamic flux measurements requires precision in isotopic sampling
and analysis, which is currently at the limit of detection. Combined with the micrometeorological gradient approach (applicable
mostly in grasslands and crop fields), stable isotope measurements allow separation of net CO2 exchange into photosynthetic and soil respiration components, and the evapotranspiration flux into soil evaporation and leaf
transpiration. Similar applications in conjunction with eddy correlation techniques (applicable to forests, in addition to
grasslands and crop fields) are more demanding, but can potentially be applied in combination with the Keeling plot relationship.
The advance and potential in using stable isotope measurements should make their use a standard component in the limited arsenal
of ecosystem-scale research tools.
Received: 8 July 1999 / Accepted: 10 January 2000 相似文献
210.