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101.
To identify potential pattern control and cell determination and/or differentiation genes in the freshwater planarian Dugesial (G.) tigrina, we searched for homeobox genes of different types in the genome of this primitive metazoan. We applied two basic approaches: 1) Screening the cDNA library with degenerate oligonucleotides corresponding to the most conserved amino acid sequence from helix-3 of the homeodomain of each family; and 2) PCR amplification of genomic DNA or cDNA, using two sets of degenerated oligonucleotides corresponding to helices 1 and 3 of the homeodomain or two specific domains of the POU family. Using the first strategy we have identified and characterized two tissue-specific cell determination and/or differentiation NK-type homeobox genes. Using the second strategy we have identified several homeobox genes that belong to the HOM/Hox, paired (prd) or POU families.  相似文献   
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Global change may substantially affect biodiversity and ecosystem functioning but little is known about its effects on essential biotic interactions. Since different environmental drivers rarely act in isolation it is important to consider interactive effects. Here, we focus on how two key drivers of anthropogenic environmental change, climate change and the introduction of alien species, affect plant–pollinator interactions. Based on a literature survey we identify climatically sensitive aspects of species interactions, assess potential effects of climate change on these mechanisms, and derive hypotheses that may form the basis of future research. We find that both climate change and alien species will ultimately lead to the creation of novel communities. In these communities certain interactions may no longer occur while there will also be potential for the emergence of new relationships. Alien species can both partly compensate for the often negative effects of climate change but also amplify them in some cases. Since potential positive effects are often restricted to generalist interactions among species, climate change and alien species in combination can result in significant threats to more specialist interactions involving native species.  相似文献   
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The binding of diamagnetic Cd(II) and paramagnetic Co(II) ions to the metal-free form of crab, Cancer pagurus, metallothionein (MT) was studied by various spectroscopic techniques. Both reconstituted and native Cd(II)-MT containing 6 mol Cd(II)/mol protein display electronic absorption, circular dichroism (CD) and magnetic circular dichroism (MCD) spectra which were indistinguishable. The stoichiometric replacement of Cd(II) ions in native Cd(II)6-MT by paramagnetic Co(II) ions enabled the geometry of the metal-binding sites to be probed. The electronic absorption and MCD spectra of Co(II)6-MT revealed features characteristic of distorted tetrahedral tetrathiolate Co(II) coordination for all six metal-binding sites. The stepwise incorporation of Cd(II) and Co(II) ions into this protein was monitored by electronic absorption and CD, and by electronic absorption and EPR spectroscopy, respectively. The results indicate that the metal-thiolate cluster structure is generated when more than four metal ions are bound. Below this titration point separate tetrahedral tetrathiolate complexes exist. This suggests that the cluster formation occurs in a two-step process. Furthermore, the spectroscopic features in both Cd(II)- and Co(II)-metal derivatives above the full metal occupancy of six suggest the existence of one additional metal-binding site. The subsequent loss of one Cd(II) ion from crab Cancer Cd(II)7-MT in the gel filtration studies demonstrate the low metal-binding affinity of the latter site. While the spectroscopic properties indicate an exclusively tetrahedral type of metal-thiolate sulfur coordination for the binding of the first six metal ions, they suggest that the seventh metal ion is coordinated in a different fashion.  相似文献   
105.
The cleavage of peptide bonds by metallopeptidases (MPs) is essential for life. These ubiquitous enzymes participate in all major physiological processes, and so their deregulation leads to diseases ranging from cancer and metastasis, inflammation, and microbial infection to neurological insults and cardiovascular disorders. MPs cleave their substrates without a covalent intermediate in a single‐step reaction involving a solvent molecule, a general base/acid, and a mono‐ or dinuclear catalytic metal site. Most monometallic MPs comprise a short metal‐binding motif (HEXXH), which includes two metal‐binding histidines and a general base/acid glutamate, and they are grouped into the zincin tribe of MPs. The latter divides mainly into the gluzincin and metzincin clans. Metzincins consist of globular ~130–270‐residue catalytic domains, which are usually preceded by N‐terminal pro‐segments, typically required for folding and latency maintenance. The catalytic domains are often followed by C‐terminal domains for substrate recognition and other protein–protein interactions, anchoring to membranes, oligomerization, and compartmentalization. Metzincin catalytic domains consist of a structurally conserved N‐terminal subdomain spanning a five‐stranded β‐sheet, a backing helix, and an active‐site helix. The latter contains most of the metal‐binding motif, which is here characteristically extended to HEXXHXXGXX(H,D). Downstream C‐terminal subdomains are generally shorter, differ more among metzincins, and mainly share a conserved loop—the Met‐turn—and a C‐terminal helix. The accumulated structural data from more than 300 deposited structures of the 12 currently characterized metzincin families reviewed here provide detailed knowledge of the molecular features of their catalytic domains, help in our understanding of their working mechanisms, and form the basis for the design of novel drugs.  相似文献   
106.
Cotton fabrics were dyed with dyes generated in situ by laccase-catalyzed oxidative coupling of the colorless 2,5-diaminobenzenesulfonic acid (2,5-DABSA) and 1-hydroxyphenol (catechol). The enzymatic oxidation of the dye intermediates led to cross-coupling reaction products when the reaction was conducted with an excess of catechol. At least fourfold excess of catechol was necessary to achieve satisfactory dye fixation on cotton. Formation of the same colored product using either an equimolar ratio of the reagents or tenfold excess of catechol was observed. Most probably, homo-molecular reactions predominate over the cross-coupling at equimolar ratio of the precursors, while with an excess of catechol, the cross-coupling occurs in higher yield. The reaction was followed using UV-Vis spectroscopy, HPLC, FTIR and MALDI-TOF MS. A reaction pathway for laccase-induced cross-coupling of catechol and 2,5-DABSA yielding a major colored product was proposed.  相似文献   
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Bacteriophage MS2 is a positive-sense, single-stranded RNA virus encapsulated in an asymmetric T = 3 pseudo-icosahedral capsid. It infects Escherichia coli through the F-pilus, in which it binds through a maturation protein incorporated into its capsid. Cryogenic electron microscopy has previously shown that its genome is highly ordered within virions, and that it regulates the assembly process of the capsid. In this study, we have assembled recombinant MS2 capsids with non-genomic RNA containing the capsid incorporation sequence, and investigated the structures formed, revealing that T = 3, T = 4 and mixed capsids between these two triangulation numbers are generated, and resolving structures of T = 3 and T = 4 capsids to 4 Å and 6 Å respectively. We conclude that the basic MS2 capsid can form a mix of T = 3 and T = 4 structures, supporting a role for the ordered genome in favouring the formation of functional T = 3 virions.  相似文献   
110.
Genomic tools are lacking for invasive and native populations of sea lamprey (Petromyzon marinus). Our objective was to discover single nucleotide polymorphism (SNP) loci to conduct pedigree analyses to quantify reproductive contributions of adult sea lampreys and dispersion of sibling larval sea lampreys of different ages in Great Lakes tributaries. Additional applications of data were explored using additional geographically expansive samples. We used restriction site‐associated DNA sequencing (RAD‐Seq) to discover genetic variation in Duffins Creek (DC), Ontario, Canada, and the St. Clair River (SCR), Michigan, USA. We subsequently developed RAD capture baits to genotype 3,446 RAD loci that contained 11,970 SNPs. Based on RAD capture assays, estimates of variance in SNP allele frequency among five Great Lakes tributary populations (mean FST 0.008; range 0.00–0.018) were concordant with previous microsatellite‐based studies; however, outlier loci were identified that contributed substantially to spatial population genetic structure. At finer scales within streams, simulations indicated that accuracy in genetic pedigree reconstruction was high when 200 or 500 independent loci were used, even in situations of high spawner abundance (e.g., 1,000 adults). Based on empirical collections of larval sea lamprey genotypes, we found that age‐1 and age‐2 families of full and half‐siblings were widely but nonrandomly distributed within stream reaches sampled. Using the genomic scale set of SNP loci developed in this study, biologists can rapidly genotype sea lamprey in non‐native and native ranges to investigate questions pertaining to population structuring and reproductive ecology at previously unattainable scales.  相似文献   
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