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1.
Hormonal imprinting takes place at the first encounter of the hormone and receptor, and results in a changed binding capacity and reaction of the cell and its progeny generations. The imprinting effect of three amino acids and their oligopeptides is studied using fluorescent-labelled peptides. Glycine and lysine could provoke positive imprinting (increased binding in the progeny generations) for their own peptides, but alanine could not. Mostly positive imprinting was provoked by glycine and lysine peptides for their own peptides of different chain length. The optimal chain length provoking self-imprinting was four for glycine, two for lysine and three for alanine. Except in this case, alanine was neutral or provoked mostly negative imprinting. After reaching the optimal chain length, there is a decline in binding. Evolutionary conclusions are discussed. 相似文献
2.
Importance of the position of TYR R boxes for repression and activation of the tyrP and aroF genes in Escherichia coli. 总被引:8,自引:8,他引:0 下载免费PDF全文
A E Andrews B Dickson B Lawley C Cobbett A J Pittard 《Journal of bacteriology》1991,173(16):5079-5085
Tyrosine-mediated repression of aroF and tyrP was studied by inserting DNA sequences between the two adjacent TYR R boxes which, in each case, overlap the respective RNA polymerase binding sites of these genes. In both cases, repression was greatest when homologous regions of these two TYR R boxes were on the same face of the DNA helix and the boxes were directly adjacent. An insertion of 3 bases was sufficient to abolish repression, which was reestablished as the boxes became separated by one full turn of the helix. These observations, coupled with the results of in vitro DNase I protection studies, supported the hypothesis that the binding of TyrR protein to the downstream boxes required cooperative interaction with TyrR protein already bound to the upstream boxes. In the case of tyrP, moving the upstream box also affected activation. Maximal activation was observed when the box was moved 3 or 12 to 14 residues upstream. Practically no activation was seen at intermediate positions, such as +7 and -4. It is hypothesized that these results indicate positions allowing maximal interaction between TyrR protein bound to the upstream box and RNA polymerase bound to the RNA polymerase binding site. 相似文献
3.
When an γ‐irradiated Dy‐, Tm‐, Sm‐ or Mn‐doped CaSO4 crystal is impulsively deformed, two peaks appear in the ML intensity versus time curve, whereby the first ML peak is found in the deformation region and the second in the post‐deformation region of the crystals. In this study, intensities Im1 and Im2 corresponding to first and second ML peaks, respectively, increased linearly with an impact velocity v0 of the piston used to deform the crystals, and times tm1 and tm2 corresponding to the first and second ML peaks, respectively, decreased with impact velocity. Total ML intensity initially increased with impact velocity and then reached a saturation value for higher values of impact velocity. ML intensity increased with increasing γ‐doses and size of crystals. Results showed that the electric field produced as a result of charging of newly‐created surfaces caused tunneling of electrons to the valence band of the hole‐trapping centres. The free holes generated moved in the valence band and their subsequent recombination with electron trapping centres released energy, thereby resulting in excitation of luminescent centres. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
Bin Jiang Jeffrey Mason Anahid Jewett Jun Qian Yijiang Ding William CS Cho Xichen Zhang Yan-gao Man 《International journal of biological sciences》2013,9(1):119-133
Background: Colorectal carcinogenesis is believed to be a multi-stage process that originates with a localized adenoma, which linearly progresses to an intra-mucosal carcinoma, to an invasive lesion, and finally to metastatic cancer. This progression model is supported by tissue culture and animal model studies, but it is difficult to reconcile with several well-established observations, principally among these are that up to 25% of early stage (Stage I/II), node-negative colorectal cancer (CRC) develop distant metastasis, and that circulating CRC cells are undetectable in peripheral blood samples of up to 50% of patients with confirmed metastasis, but more than 30% of patients with no detectable metastasis exhibit such cells. The mechanism responsible for this diverse behavior is unknown, and there are no effective means to identify patients with pending, or who are at high risk for, developing metastatic CRC.Novel findings: Our previous studies of human breast and prostate cancer have shown that cancer invasion arises from the convergence of a tissue injury, the innate immune response to that injury, and the presence of tumor stem cells within tumor capsules at the site of the injury. Focal degeneration of a capsule due to age or disease attracts lymphocyte infiltration that degrades the degenerating capsules resulting in the formation of a focal disruption in the capsule, which selectively favors proliferating or “budding” of the underlying tumor stem cells. Our recent studies suggest that lymphocyte infiltration also triggers metastasis by disrupting the intercellular junctions and surface adhesion molecules within the proliferating cell buds causing their dissociation. Then, lymphocytes and tumor cells are conjoined through membrane fusion to form tumor-lymphocyte chimeras (TLCs) that allows the tumor stem cell to avail itself of the lymphocyte''s natural ability to migrate and breach cell barriers in order to intravasate and to travel to distant organs. Our most recent studies of human CRC have detected nearly identical focal capsule disruptions, lymphocyte infiltration, budding cells, and the formation of TLCs. Our studies have further shown that age- and type-matched node-positive and -negative CRC have a significantly different morphological and immunohistochemical profile and that the majority of lymphatic ducts with disseminated cells are located within the mucosa adjacent to morphologically normal appearing epithelial structures that express a stem cell-related marker.New hypothesis: Based on these findings and the growth patterns of budding cells revealed by double immunohistochemistry, we further hypothesize that metastatic spread is an early event of carcinogenesis and that budding cells overlying focal capsule disruptions represent invasion- and metastasis-initiating cells that follow one of four pathways to progress: (1) to undergo extensive in situ proliferation leading to the formation of tumor nests that subsequently invade the submucosa, (2) to migrate with associated lymphocytes functioning as “seeds” to grow in new sites, (3) to migrate and intravasate into pre-existing vascular structures by forming TLCs, or (4) to intravasate into vascular structures that are generated by the budding cells themselves. We also propose that only node-positive cases harbor stem cells with the potential for multi-lineage differentiation and unique surface markers that permit intravasation. 相似文献
5.
6.
P-type ATPase heavy metal transporters with roles in essential zinc homeostasis in Arabidopsis 总被引:20,自引:0,他引:20 下载免费PDF全文
Hussain D Haydon MJ Wang Y Wong E Sherson SM Young J Camakaris J Harper JF Cobbett CS 《The Plant cell》2004,16(5):1327-1339
Arabidopsis thaliana has eight genes encoding members of the type 1B heavy metal–transporting subfamily of the P-type ATPases. Three of these transporters, HMA2, HMA3, and HMA4, are closely related to each other and are most similar in sequence to the divalent heavy metal cation transporters of prokaryotes. To determine the function of these transporters in metal homeostasis, we have identified and characterized mutants affected in each. Whereas the individual mutants exhibited no apparent phenotype, hma2 hma4 double mutants had a nutritional deficiency phenotype that could be compensated for by increasing the level of Zn, but not Cu or Co, in the growth medium. Levels of Zn, but not other essential elements, in the shoot tissues of a hma2 hma4 double mutant and, to a lesser extent, of a hma4 single mutant were decreased compared with the wild type. Together, these observations indicate a primary role for HMA2 and HMA4 in essential Zn homeostasis. HMA2promoter- and HMA4promoter-reporter gene constructs provide evidence that HMA2 and HMA4 expression is predominantly in the vascular tissues of roots, stems, and leaves. In addition, expression of the genes in developing anthers was confirmed by RT-PCR and was consistent with a male-sterile phenotype in the double mutant. HMA2 appears to be localized to the plasma membrane, as indicated by protein gel blot analysis of membrane fractions using isoform-specific antibodies and by the visualization of an HMA2-green fluorescent protein fusion by confocal microscopy. These observations are consistent with a role for HMA2 and HMA4 in Zn translocation. hma2 and hma4 mutations both conferred increased sensitivity to Cd in a phytochelatin-deficient mutant background, suggesting that they may also influence Cd detoxification. 相似文献
7.
Two alpha-L-arabinofuranosidase genes in Arabidopsis thaliana are differentially expressed during vegetative growth and flower development 总被引:1,自引:0,他引:1
Glycosyl hydrolases are important mediators of plant cell wall modification during plant development. These enzymes catalyse the hydrolytic release of specific sugars, such as L-arabinose, from the polysaccharide-rich cell wall matrix. The cloning and expression analysis of two genes, AtASD1 and AtASD2, encoding putative alpha-L-arabinofuranosidases in Arabidopsis thaliana are reported here. AtASD1 and AtASD2 identities were assigned on the basis of homology to plant and microbial family 51 glycoside hydrolases. Using RT-PCR, RNA gel blot analysis and reporter gene expression analysis, AtASD1 and AtASD2 were shown to have different developmental expression profiles. High levels of AtASD1 promoter activity are present in multiple tissues during vegetative and reproductive growth. AtASD1 expression is particularly intense in zones of cell proliferation, the vascular system, developing and regressing floral tissues, and floral abscission zones. By comparison, AtASD2 expression is limited to the vasculature of older root tissue and to some floral organs and floral abscission zones. 相似文献
8.
The correlation of protein structure and evolution of a protein-coding gene: phylogenetic inference using cytochrome oxidase III 总被引:1,自引:1,他引:0
Discriminating phylogenetic signal from noise in DNA sequence data is a
difficult problem in phylogenetic inference at higher systematic levels.
For protein-coding genes, noise at synonymous (silent) positions can be
filtered by deleting entire codon positions or types of change at a codon
position. This method is not appropriate for replacement sites, because
changes at each site within a codon may not be independent. This research
presents a method using information from protein structure to evaluate
variation in replacement sites. Analysis of the correlation of amino acid
variation with protein structure identified rapidly evolving codons in the
COIII gene. In a series of phylogenetic analyses attempting to recover a
known set of vertebrate relationships, downweighting these labile codons
produced the most accurate results. Structural correlates of variable and
invariant residues identified in this study can be used to increase the
accuracy of models used for phylogenetic inference. Viewing amino acid
variation within a phylogenetic framework provided insight into residue
changes important in the secondary and tertiary structures of the molecule,
changes that were correlated between pairs of neighboring residues or
between residues in neighboring helices.
相似文献
9.
Christopher S. Cobbett Mike J. May Ross Howden Barbara Rolls 《The Plant journal : for cell and molecular biology》1998,16(1):73-78
This paper reports that the glutathione (GSH)-deficient mutant, cad2–1 , of Arabidopsis is deficient in the first enzyme in the pathway of GSH biosynthesis, γ-glutamylcysteine synthetase (GCS). The mutant accumulates a substrate of GCS, cysteine, and is deficient in the product, γ-glutamylcysteine. In vitro enzyme assays showed that the cad2–1 mutant has 40% of wild-type levels of GCS activity but is unchanged in the activity of the second enzyme in the pathway, GSH synthetase. The CAD2 locus maps to chromosome 4 and is tightly linked to a gene, GSHA , identified by a previously isolated cDNA. A genomic clone of GSHA complements both the phenotypic and biochemical deficiencies of the cad2–1 mutant. The nucleotide sequence of the gene has been determined and, in the mutant, this gene contains a 6 bp deletion within an exon. These data demonstrate that the CAD2 gene encodes GCS. The cad2–1 mutation is close to the conserved cysteine which is believed to bind the substrate glutamate and the specific inhibitor L-buthionine-[S,R] sulfoximine (BSO). Both root growth and GCS activity of the cad2–1 mutant was less sensitive than the wild-type to inhibition by BSO, indicating that the mutation may alter the affinity of the inhibitor binding site. 相似文献
10.
Andréia S Lessa Bruno D Paredes Juliana V Dias Adriana B Carvalho Luiz Fernando Quintanilha Christina M Takiya Bernardo R Tura Guilherme FM Rezende Antonio C Campos de Carvalho Célia MC Resende Regina CS Goldenberg 《BMC veterinary research》2010,6(1):1-10