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231.
Low-fidelity DNA synthesis by human DNA polymerase theta 总被引:2,自引:1,他引:1
Human DNA polymerase theta (pol θ or POLQ) is a proofreading-deficient family A enzyme implicated in translesion synthesis (TLS) and perhaps in somatic hypermutation (SHM) of immunoglobulin genes. These proposed functions and kinetic studies imply that pol θ may synthesize DNA with low fidelity. Here, we show that when copying undamaged DNA, pol θ generates single base errors at rates 10- to more than 100-fold higher than for other family A members. Pol θ adds single nucleotides to homopolymeric runs at particularly high rates, exceeding 1% in certain sequence contexts, and generates single base substitutions at an average rate of 2.4 × 10−3, comparable to inaccurate family Y human pol κ (5.8 × 10−3) also implicated in TLS. Like pol κ, pol θ is processive, implying that it may be tightly regulated to avoid deleterious mutagenesis. Pol θ also generates certain base substitutions at high rates within sequence contexts similar to those inferred to be copied by pol θ during SHM of immunoglobulin genes in mice. Thus, pol θ is an exception among family A polymerases, and its low fidelity is consistent with its proposed roles in TLS and SHM. 相似文献
232.
Fredrik Dalerum Michael J. Somers Kyran E. Kunkel Elissa Z. Cameron 《Biodiversity and Conservation》2008,17(12):2939-2949
Biodiversity in southern Africa is globally extraordinary but threatened by human activities. Although there are considerable
biodiversity conservation initiatives within the region, no one has yet assessed the potential use of large carnivores in
such actions. Surrogate approaches have often been suggested as one such way of capitalizing on large carnivores. Here we
review the suitability of the large carnivore guild (i.e., brown hyaena Hyaena hyaena, spotted hyaena Crocuta crocutta, cheetah Acinonyx jubatus, leopard Panthera pardus, lion Panthea leo and African wild dog Lycaon pictus) to act as surrogate species for biodiversity conservation in southern Africa. We suggest that the guild must be complete
for the large carnivores to fully provide their role as ecological keystones. The potential for large carnivores to act as
umbrella and indicator species seems limited. However, self-sustaining populations of large carnivores may be useful indicators
of unfragmented landscapes. Moreover, diversity within the large carnivore guild may reflect overall biodiversity. Although
the global appeal of the large African carnivores makes them important international flagships, we stress that international
conservation funding must be linked to local communities for them to be important also locally. In summary, we suggest that
the flagship value of these large carnivores should be used to promote biodiversity conservation in the region, and that the
suggested relationship between large carnivore diversity and overall biodiversity is empirically tested. Finally we suggest
that direct conservation activities should focus on enhancing the keystone values of large carnivores through complete guild
conservation and restoration. 相似文献
233.
234.
Lipid-free NisI: interaction with nisin and contribution to nisin immunity via secretion 总被引:1,自引:0,他引:1
Timo M. Takala Olli Koponen Mingqiang Qiao Per E.J. Saris 《FEMS microbiology letters》2004,237(1):171-177
Nisin-producing Lactococcus lactis cells protect their own cytoplasmic membrane by specific immunity proteins, NisF/E/G and NisI, a transporter complex and a lipoprotein, respectively. A portion of NisI is secreted to the medium in a lipid-free form (LF-NisI). Here, kinetics of the interaction between nisin and LF-NisI was examined by surface plasmon resonance analysis. The affinity constant KD for the interaction was calculated to be in the micromolar range. Contribution of the secreted LF-NisI to nisin immunity was studied by replacing the lipoprotein specific nisI signal sequence with a secretion signal of non-lipoprotein origin. Secretion of LF-NisI in NisF/E/G-expressing L. lactis strain NZ9840 increased significantly its nisin tolerance suggesting that the lipid-free form of NisI could have a supportive role in nisin immunity. 相似文献
235.
Response of zooplankton to nutrient enrichment and fish in shallow lakes: a pan-European mesocosm experiment 总被引:5,自引:1,他引:4
Kirsi Vakkilainen Timo Kairesalo Jaana Hietala David M. Balayla Eloy Bécares Wouter J. Van de Bund Ellen Van Donk Margarita Fernández-Aláez Mikael Gyllström Lars-Anders Hansson Maria R. Miracle Brian Moss Susana Romo Juan Rueda Deborah Stephen 《Freshwater Biology》2004,49(12):1619-1632
1. Responses of zooplankton to nutrient enrichment and fish predation were studied in 1998 and 1999 by carrying out parallel mesocosm experiments in six lakes across Europe. 2. Zooplankton community structure, biomass and responses to nutrient and fish manipulation showed geographical and year‐to‐year differences. Fish had a greater influence than nutrients in regulating zooplankton biomass and especially the relative abundances of different functional groups of zooplankton. When fish reduced the biomass of large crustaceans, there was a complementary increase in the biomasses of smaller crustacean species and rotifers. 3. High abundance of submerged macrophytes provided refuge for zooplankton against fish predation but this refuge effect differed notably in magnitude among sites. 4. Large crustacean grazers (Daphnia, Diaphanosoma, Sida and Simocephalus) were crucial in controlling algal biomass, while smaller crustacean grazers and rotifers were of minor importance. Large grazers were able to control phytoplankton biomass even under hypereutrophic conditions (up to 1600 μg TP L?1) when grazer biomass was high (>80–90 μg dry mass L?1) or accounted for >30% of the grazer community. 5. The littoral zooplankton community was less resistant to change following nutrient enrichment in southern Spain, at high temperatures (close to 30 °C), than at lower temperatures (17–23 °C) characterising the other sites. This lower resistance was because of a greater importance of nutrients than zooplankton in controlling algal biomass. 6. Apart from the reduced role of large crustacean grazers at the lowest latitude, no consistent geographical patterns were observed in the responses of zooplankton communities to nutrient and fish manipulation. 相似文献
236.
Hagren V von Lode P Syrjälä A Soukka T Lövgren T Kojola H Nurmi J 《Analytical biochemistry》2008,374(2):411-416
We have developed a novel instrument platform, GenomEra, for small-scale analysis of nucleic acids. The platform combines a rapid thermal cycler, an integrated time-resolved fluorescence measurement unit, and user-friendly software for the analysis of results. Disposable low-cost plastic reaction vessels are designed specifically for the instrument and contain all of the assay-specific reagents in dry form. The appropriate assay protocol is specified on barcodes printed under the vessels and is automatically initiated by the software. Detection is based on the use of sequence-specific probes labeled with intrinsically fluorescent europium or terbium chelates and complementary quencher probes, which enable sensitive, homogeneous closed-tube assays without the risk of carryover contamination. The detection limit of the instrument (background + 3 SD) is approximately 20 pmol/L for both chelates with a dynamic range of nearly four orders of magnitude. The functionality of the platform is demonstrated with a dual-label homogeneous polymerase chain reaction (PCR) assay for the detection of Salmonella using a Magda CA Salmonella assay kit. An internal amplification control is included in each reaction to eliminate false negative results caused by PCR inhibition. Qualitative assay results are automatically interpreted by the software and are available 45 min after sample addition. 相似文献
237.
Zaidi N Hermann C Herrmann T Kalbacher H 《Biochemical and biophysical research communications》2008,377(2):327-330
Cathepsin E is an intracellular aspartic protease of the endolysosomal pathway. It has been implicated in several physiological and pathological processes however, its exact functional role is yet to be elucidated. The present review gives an account of the major physiological functions that are associated to cathepsin E by various research groups and highlights the conditions developed in cathepsin E deficiency or the conditions where overexpression of cathepsin E is observed. 相似文献
238.
Burster T Reich M Zaidi N Voelter W Boehm BO Kalbacher H 《Biochemical and biophysical research communications》2008,377(4):1299-1303
Processing of antigens by proteases in the endocytic compartments of antigen presenting cells (APC) is essential to make them suitable for presentation as antigenic peptides to T lymphocytes. Several proteases of the cysteine, aspartyl and serine classes are involved in this process. It has been speculated, that the aspartyl protease cathepsin E (CatE) is involved in antigen processing in B cell line, monocyte-derived dendritic cells (DC) and murine DC. Here we show the expression of CatE in primary human B cells and DC, which was only elevated in B cells after induction with phorbol 12-myristate 13-acetate (PMA), resulted in enhanced presentation of tetanus toxin C-fragment (TTC) to the respective T cells. Inhibition of aspartyl proteases using pepstatin-A-penetratin (PepA-P), a highly efficient, cell-permeable aspartyl protease inhibitor, reduced significantly T cell activation in PMA activated B cells but not in PMA activated myeloid DC (mDC). Thus we suggest that CatE is important in the processing of TTC in primary human B cells. 相似文献
239.
Bactericidal properties of human and murine groups I, II, V, X, and XII secreted phospholipases A(2). 总被引:5,自引:0,他引:5
Rao S Koduri Juha O Gr?nroos Veli J O Laine Catherine Le Calvez Gérard Lambeau Timo J Nevalainen Michael H Gelb 《The Journal of biological chemistry》2002,277(8):5849-5857
Group IIA secreted phospholipase A(2) (sPLA2) is known to display potent Gram-positive bactericidal activity in vitro and in vivo. We have analyzed the bactericidal activity of the full set of recombinant murine and human groups I, II, V, X, and XII sPLA2s on Listeria monocytogenes, Staphylococcus aureus, and Escherichia coli. The rank order potency among human sPLA2s against Gram-positive bacteria is group IIA > X > V > XII > IIE > IB, IIF (for murine sPLA2s: IIA > IID > V > IIE > IIC, X > IB, IIF), and only human group XII displays detectable bactericidal activity against the Gram-negative bacterium E. coli. These studies show that highly basic sPLA2s display potent bactericidal activity with the exception of the ability of the acidic human group X sPLA2 to kill Gram-positive bacteria. By studying the Bacillus subtilis and S. aureus bactericidal potencies of a large panel of human group IIA mutants in which basic residues were mutated to acidic residues, it was found that: 1) the overall positive charge of the sPLA2 is the dominant factor in dictating bactericidal potency; 2) basic residues on the putative membrane binding surface of the sPLA2 are modestly more important for bactericidal activity than are other basic residues; 3) relative bactericidal potency tracks well with the ability of these mutants to degrade phospholipids in the bacterial membrane; and 4) exposure of the bacterial membrane of Gram-positive bacteria by disruption of the cell wall dramatically reduces the negative effect of charge reversal mutagenesis on bactericidal potency. 相似文献
240.
Effect of Genetically Modified Pseudomonas putida WCS358r on the Fungal Rhizosphere Microflora of Field-Grown Wheat 总被引:3,自引:0,他引:3
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Debora C. M. Glandorf Patrick Verheggen Timo Jansen Jan-Willem Jorritsma Eric Smit Paula Leeflang Karel Wernars Linda S. Thomashow Eric Laureijs Jane E. Thomas-Oates Peter A. H. M. Bakker Leendert C. van Loon 《Applied microbiology》2001,67(8):3371-3378
We released genetically modified Pseudomonas putida WCS358r into the rhizospheres of wheat plants. The two genetically modified derivatives, genetically modified microorganism (GMM) 2 and GMM 8, carried the phz biosynthetic gene locus of strain P. fluorescens 2-79 and constitutively produced the antifungal compound phenazine-1-carboxylic acid (PCA). In the springs of 1997 and 1998 we sowed wheat seeds treated with either GMM 2, GMM 8, or WCS358r (approximately 107 CFU per seed), and measured the numbers, composition, and activities of the rhizosphere microbial populations. During both growing seasons, all three bacterial strains decreased from 107 CFU per g of rhizosphere sample to below the limit of detection (102 CFU per g) 1 month after harvest of the wheat plants. The phz genes were stably maintained, and PCA was detected in rhizosphere extracts of GMM-treated plants. In 1997, but not in 1998, fungal numbers in the rhizosphere, quantified on 2% malt extract agar (total filamentous fungi) and on Komada's medium (mainly Fusarium spp.), were transiently suppressed in GMM 8-treated plants. We also analyzed the effects of the GMMs on the rhizosphere fungi by using amplified ribosomal DNA restriction analysis. Introduction of any of the three bacterial strains transiently changed the composition of the rhizosphere fungal microflora. However, in both 1997 and 1998, GMM-induced effects were distinct from those of WCS358r and lasted for 40 days in 1997 and for 89 days after sowing in 1998, whereas effects induced by WCS358r were detectable for 12 (1997) or 40 (1998) days. None of the strains affected the metabolic activity of the soil microbial population (substrate-induced respiration), soil nitrification potential, cellulose decomposition, plant height, or plant yield. The results indicate that application of GMMs engineered to have improved antifungal activity can exert nontarget effects on the natural fungal microflora. 相似文献