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141.
The ATP-binding-cassette transmembrane transporters (ABC transporters)
known from vertebrates belong to four major subfamilies: (1) the P-
glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance
regulators (CFTR); (3) the Tap proteins encoded with the major
histocompatibility complex of mammals; and (4) the peroxisomal membrane
proteins. Both Pgp and CFTR have a structure suggesting a past internal
gene duplication; a phylogenetic analysis indicated that these duplications
occurred independently, while an independent tandem gene duplication
occurred in the case of the Tap family. Both the Pgp and Tap proteins show
evidence of relationship to bacterial ABC transporters lacking internal
duplication, and both are significantly more closely related to the HlyB
and MsbA families of transporters from purple bacteria than they are to ABC
transporters from nonpurple bacteria. The simplest hypothesis to explain
this observation is that eukaryotic Pgp and Tap genes are descended from a
mitochondrial gene or genes that were subsequently translocated to the
nuclear genome. The Pgp genes of eukaryotes are characterized by a
remarkable degree of convergent evolution between the ATP-binding cassettes
of their N- terminal and C-terminal halves, whereas no such convergence is
seen between the two halves of CFTR genes or between the duplicated Tap
genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain
not found in other ABC transporters apart from CFTR, showed high levels of
both synonymous and nonsynonymous difference in comparisons among different
mammalian species, suggesting that this region is a mutational hot spot.
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Abstract: A moderately thermophilic mixed culture of bacteria catalysed the oxidative solubilization of arsenopyrite to give Fe(III), S(VI) and As(V). Toxic effects were observed in a few experiments due to teh build-up of As(III). The bacterial oxidation of arsenopyrite involved direct attack of the bacteria on the mineral to give AS(III). Subsequent oxidation of AS(III) to AS(V) occurred reaction with FE(III), but only in the presence of pyrite, which provide a catalytic surface. Arsenopyrite was unable to act as a catalyst. The pyrite- catalysed oxidation of As(III) to AS(V) by FE(III) usually only went to completion in the presence of bacteria, possibly due to their role in the provision of clean catalytic surfaces. Thus, toxic concentrations of As(III) may accumulate in reactors during the bacterial oxidation of arsenopyrite due to the absence of pyrite or a clean pyrite surface or to low concentrations of the effective oxidizing agent, Fe(III). 相似文献
145.
Replication of human papillomavirus (HPV) DNA requires the viral proteins E1 and E2. Amino acid similarities to SV40 large-T antigen had suggested that E1 is a DNA helicase/ATPase involved in initiating viral DNA replication, and this has recently been shown for bovine papillomavirus type 1 (BPV-1) E1 protein. However, in vitro analysis of HPV E1 has been hampered by the inability to produce purified protein using heterologous expression systems. We have succeeded in demonstrating ATPase and DNA helicase activities in purified HPV E1, expressed in E. coli as a maltose-binding protein fusion (MBP-E1), for the first time. As further confirmation that the ATPase and DNA helicase activities are due to E1 and not contaminating E. coli enzymes, we have shown that a fusion protein containing an amino acid change (E1 Pro-479 to Ser), predicted to inactivate ATP-binding, has impaired activities. We have carried out a structure prediction analysis which suggests that E1 may form two domains: a relatively open N-terminal domain (residues 1-125), and a highly structured C-terminal domain (170-649), with an intermediate region (125-170) predicted to form an inter-domain linker. This is consistent with the proteolytic susceptibility of MBP-E1 at a site 15-20 kD from the N-terminus of E1, and the accumulation of a 58 kD C-terminal fragment of E1. We speculate that the N-terminal domain is involved in DNA-binding, while the C-terminal 58 kD may constitute a distinct enzymatic domain. HPV E1 is of interest as a therapeutic target and the availability of pure enzyme will be invaluable in the search for antiviral compounds. 相似文献
146.
Carles Ibáñez Nuno Caiola José Barquín Oscar Belmar Xavier Benito-Granell Frederic Casals Siobhan Fennessy Jocelyne Hughes Margaret Palmer Josep Peñuelas Estela Romero Jordi Sardans Michael Williams 《Global Change Biology》2023,29(5):1248-1266
Trends and ecological consequences of phosphorus (P) decline and increasing nitrogen (N) to phosphorus (N:P) ratios in rivers and estuaries are reviewed and discussed. Results suggest that re-oligotrophication is a dominant trend in rivers and estuaries of high-income countries in the last two–three decades, while in low-income countries widespread eutrophication occurs. The decline in P is well documented in hundreds of rivers of United States and the European Union, but the biotic response of rivers and estuaries besides phytoplankton decline such as trends in phytoplankton composition, changes in primary production, ecosystem shifts, cascading effects, changes in ecosystem metabolism, etc., have not been sufficiently monitored and investigated, neither the effects of N:P imbalance. N:P imbalance has significant ecological effects that need to be further investigated. There is a growing number of cases in which phytoplankton biomass have been shown to decrease due to re-oligotrophication, but the potential regime shift from phytoplankton to macrophyte dominance described in shallow lakes has been documented only in a few rivers and estuaries yet. The main reasons why regime shifts are rarely described in rivers and estuaries are, from one hand the scarcity of data on macrophyte cover trends, and from the other hand physical factors such as peak flows or high turbidity that could prevent a general spread of submerged macrophytes as observed in shallow lakes. Moreover, re-oligotrophication effects on rivers may be different compared to lakes (e.g., lower dominance of macrophytes) or estuaries (e.g., limitation of primary production by N instead of P) or may be dependent on river/estuary type. We conclude that river and estuary re-oligotrophication effects are complex, diverse and still little known, and in some cases are equivalent to those described in shallow lakes, but the regime shift is more likely to occur in mid to high-order rivers and shallow estuaries. 相似文献
147.
Within estuarine and coastal ecosystems globally, extensive habitat degradation and loss threaten critical ecosystem functions and necessitate widescale restoration efforts. There is abundant evidence that ecological processes and species interactions can vary with habitat characteristics, which has important implications for the design and implementation of restoration efforts aimed at enhancing specific ecosystem functions and services. We conducted an experiment examining how habitat characteristics (presence; edge vs. interior) influence the communities of resident fish and mobile invertebrates on restored oyster (Crassostrea virginica) reefs. Similar to previous studies, we found that restored reefs altered community composition and augmented total abundance and biomass relative to unstructured sand habitat. Community composition and biomass also differed between the edge and interior of individual reefs as a result of species-specific patterns over small spatial scales. These patterns were only weakly linked to oyster density, suggesting that other factors that vary between edge and interior (e.g. predator access or species interactions) are likely more important for community structure on oyster reefs. Fine-scale information on resident species' use of oyster reefs will help facilitate restoration by allowing decision makers to optimize the amount of edge versus interior habitat. To improve the prediction of faunal use and benefits from habitat restoration, we recommend investigations into the mechanisms shaping edge and interior preferences on oyster reefs. 相似文献
148.
Liam J. Hughes Oscar Morton Brett R. Scheffers David P. Edwards 《Biological reviews of the Cambridge Philosophical Society》2023,98(3):775-791
Wildlife trade is a key driver of extinction risk, affecting at least 24% of terrestrial vertebrates. The persistent removal of species can have profound impacts on species extinction risk and selection within populations. We draw together the first review of characteristics known to drive species use – identifying species with larger body sizes, greater abundance, increased rarity or certain morphological traits valued by consumers as being particularly prevalent in trade. We then review the ecological implications of this trade-driven selection, revealing direct effects of trade on natural selection and populations for traded species, which includes selection against desirable traits. Additionally, there exists a positive feedback loop between rarity and trade and depleted populations tend to have easy human access points, which can result in species being harvested to extinction and has the potential to alter source–sink dynamics. Wider cascading ecosystem repercussions from trade-induced declines include altered seed dispersal networks, trophic cascades, long-term compositional changes in plant communities, altered forest carbon stocks, and the introduction of harmful invasive species. Because it occurs across multiple scales with diverse drivers, wildlife trade requires multi-faceted conservation actions to maintain biodiversity and ecological function, including regulatory and enforcement approaches, bottom-up and community-based interventions, captive breeding or wildlife farming, and conservation translocations and trophic rewilding. We highlight three emergent research themes at the intersection of trade and community ecology: (1) functional impacts of trade; (2) altered provisioning of ecosystem services; and (3) prevalence of trade-dispersed diseases. Outside of the primary objective that exploitation is sustainable for traded species, we must urgently incorporate consideration of the broader consequences for other species and ecosystem processes when quantifying sustainability. 相似文献
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