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61.
Jens G. P. Diller Sophia Drescher Mario Hofmann Max Rabus Heike Feldhaar Christian Laforsch 《Ecology and evolution》2022,12(4)
Invasive alien species are a major threat to ecosystems. Invasive terrestrial plants can produce allelochemicals which suppress native terrestrial biodiversity. However, it is not known if leached allelochemicals from invasive plants growing in riparian zones, such as Impatiens glandulifera, also affect freshwater ecosystems. We used mesocosms and laboratory experiments to test the impact of I. glandulifera on a simplified freshwater food web. Our mesocosm experiments show that leachate from I. glandulifera significantly reduced population growth rate of the water flea Daphnia magna and the green alga Acutodesmus obliquus, both keystone species of lakes and ponds. Laboratory experiments using the main allelochemical released by I. glandulifera, 2‐methoxy‐1,4‐naphthoquinone, revealed negative fitness effects in D. magna and A. obliquus. Our findings show that allelochemicals from I. glandulifera not only reduce biodiversity in terrestrial habitats but also pose a threat to freshwater ecosystems, highlighting the necessity to incorporate cross‐ecosystem effects in the risk assessment of invasive species. 相似文献
62.
Mycobacterium tuberculosis, along with other actinobacteria, harbours proteasomes in addition to members of the general bacterial repertoire of degradation complexes. In analogy to ubiquitination in eukaryotes, substrates are tagged for proteasomal degradation with prokaryotic ubiquitin‐like protein (Pup) that is recognized by the N‐terminal coiled‐coil domain of the ATPase Mpa (also called ARC). Here, we reconstitute the entire mycobacterial proteasome degradation system for pupylated substrates and establish its mechanistic features with respect to substrate recruitment, unfolding and degradation. We show that the Mpa–proteasome complex unfolds and degrades Pup‐tagged proteins and that this activity requires physical interaction of the ATPase with the proteasome. Furthermore, we establish the N‐terminal region of Pup as the structural element required for engagement of pupylated substrates into the Mpa pore. In this process, Mpa pulls on Pup to initiate unfolding of substrate proteins and to drag them toward the proteasome chamber. Unlike the eukaryotic ubiquitin, Pup is not recycled but degraded with the substrate. This assigns a dual function to Pup as both the Mpa recognition element as well as the threading determinant. 相似文献
63.
Introns are generally believed to evolve too rapidly and too erratically to be of much use in phylogenetic reconstructions.
Few phylogenetically informative intron sequences are available, however, to ascertain the validity of this supposition. In
the present study the supposition was tested on the example of the mammalian class II major histocompatibility complex (Mhc) genes of the DRB family. Since the Mhc genes evolve under balancing selection and are believed to recombine or rearrange frequently, the evolution of their introns
could be expected to be particularly rapid and subject to scrambling. Sequences of intron 4 and 5 DRB genes were obtained from polymerase chain reaction-amplified fragments of genomic DNA from representatives of six eutherian
orders—Primates, Scandentia, Chiroptera, Dermoptera, Lagomorpha, and Insectivora. Although short stretches of the introns
have indeed proved to be unalignable, the bulk of the intron sequences from all six orders, spanning >85 million years (my)
of evolution, could be aligned and used in a study of the tempo and mode of intron evolution. The analysis has revealed the
Mhc introns to evolve at a rate similar to that of other genes and of synonymous sites of non-Mhc genes. No evidence of homogenization or large-scale scrambling of the intron sequences could be found. The Mhc introns apparently evolve largely by point mutations and insertions/deletions. The phylogenetic signals contained in the
intron sequences could be used to identify Scandentia as the sister group of Primates, to support the existence of the Archonta
superorder, and to confirm the monophyly of the Chiroptera.
Received: 26 October 1998 / Accepted: 21 December 1998 相似文献
64.
Nishinakamura R Matsumoto Y Matsuda T Ariizumi T Heike T Asashima M Yokota T 《Developmental biology》1999,216(2):481-490
Stat3 is one of the main signaling components of cytokine receptors, including gp130. Here we show that activation of cytokine receptor gp130 resulted in a dramatic ventralization of Xenopus embryos and that the ventralization correlated well with Stat3 activation potential of the receptor. This finding led to identification of Xenopus Stat3 (Xstat3), which showed a 95% homology to its murine and human counterparts, at the amino acid level, and was expressed from the one-cell stage throughout development. The mechanism of gp130/XStat3-mediated ventralization proved to be independent of BMP-4. gp130/Xstat3 stimulation inhibited Smad2-induced ectopic axis formation in embryos and Smad2-dependent luciferase activity. A dominant-negative Stat3, in contrast, dorsalized Xenopus embryos, resulting in ectopic axis formation. We propose that Stat3-mediated signaling has the capacity to modify dorsoventral patterning in the early development of Xenopus. 相似文献
65.
Bauer Paul J.; Schauf Heike; Schwarzer Andreas; Brown Joel E. 《American journal of physiology. Cell physiology》1999,276(3):C558
Na+/Ca2+exchange has been investigated in squid(Loligopealei) rhabdomeric membranes.Ca2+-containing vesicles have beenprepared from purified rhabdomeric membranes by extrusion throughpolycarbonate filters of 1-µm pore size. After removal of externalCa2+, up to 90% of the entrappedCa2+ could be specificallyreleased by the addition of Na+;this finding indicates that most of the vesicles containedNa+/Ca2+exchanger. The Na+-inducedCa2+ efflux had a half-maximumvalue (K1/2) of~44 mM and a Hill coefficient of ~1.7. The maximalNa+-inducedCa2+ efflux was ~0.6 nmolCa2+ · s1 · mgprotein1. SimilarNa+-inducedCa2+ effluxes were measured ifK+ was replaced withLi+ orCs+. Vesicles loaded withCa2+ byNa+/Ca2+exchange also released this Ca2+byNa+/Ca2+exchange, suggesting thatNa+/Ca2+exchange operated in both forward and reverse modes. Limited proteolysis by trypsin resulted in a rate ofCa2+ efflux enhanced byapproximately fivefold when efflux was activated with 95 mM NaCl. For vesicles subjected to limited proteolysis by trypsin,Na+/Ca2+exchange was characterized by aK1/2 of ~25 mMand a Hill coefficient of 1.6. For these vesicles, the maximalNa+-inducedCa2+ efflux was about twice asgreat as in control vesicles. We conclude thatNa+/Ca2+exchange proteins localized in rhabdomeric membranes mediate Ca2+ extrusion in squid photoreceptors. 相似文献
66.
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68.
Cottrell SE Distler J Goodman NS Mooney SH Kluth A Olek A Schwope I Tetzner R Ziebarth H Berlin K 《Nucleic acids research》2004,32(1):e10
DNA methylation-based biomarkers have been discovered that could potentially be used for the diagnosis of cancer by detection of circulating, tumor-derived DNA in bodily fluids. Any methylation detection assay that would be applied to these samples must be capable of detecting small amounts of tumor DNA in the presence of background normal DNA. We have developed a real-time PCR assay, called HeavyMethyl, that is well suited for this application. HeavyMethyl uses methylation-specific oligonucleotide blockers and a methylation-specific probe to achieve methylation-specific amplification and detection. We tested the assays on unmethylated and artificially methylated DNA in order to determine the limit of detection. After careful optimization, our glutathione-S-transferase pi1 and Calcitonin assays can amplify as little as 30 and 60 pg of methylated DNA, respectively, and neither assay amplifies unmethylated DNA. The Calcitonin assay showed a highly significant methylation difference between normal colon and colon adenocarcinomas, and methylation was also detected in serum DNA from colon cancer patients. These assays show that HeavyMethyl technology can be successfully employed for the analysis of very low concentrations of methylated DNA, e.g. in serum of patients with tumors. 相似文献
69.
70.
Paal J Henselewski H Muth J Meksem K Menéndez CM Salamini F Ballvora A Gebhardt C 《The Plant journal : for cell and molecular biology》2004,38(2):285-297
The endoparasitic root cyst nematode Globodera rostochiensis causes considerable damage in potato cultivation. In the past, major genes for nematode resistance have been introgressed from related potato species into cultivars. Elucidating the molecular basis of resistance will contribute to the understanding of nematode-plant interactions and assist in breeding nematode-resistant cultivars. The Gro1 resistance locus to G. rostochiensis on potato chromosome VII co-localized with a resistance-gene-like (RGL) DNA marker. This marker was used to isolate from genomic libraries 15 members of a closely related candidate gene family. Analysis of inheritance, linkage mapping, and sequencing reduced the number of candidate genes to three. Complementation analysis by stable potato transformation showed that the gene Gro1-4 conferred resistance to G. rostochiensis pathotype Ro1. Gro1-4 encodes a protein of 1136 amino acids that contains Toll-interleukin 1 receptor (TIR), nucleotide-binding (NB), leucine-rich repeat (LRR) homology domains and a C-terminal domain with unknown function. The deduced Gro1-4 protein differed by 29 amino acid changes from susceptible members of the Gro1 gene family. Sequence characterization of 13 members of the Gro1 gene family revealed putative regulatory elements and a variable microsatellite in the promoter region, insertion of a retrotransposon-like element in the first intron, and a stop codon in the NB coding region of some genes. Sequence analysis of RT-PCR products showed that Gro1-4 is expressed, among other members of the family including putative pseudogenes, in non-infected roots of nematode-resistant plants. RT-PCR also demonstrated that members of the Gro1 gene family are expressed in most potato tissues. 相似文献