933 resultados para evolving
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In an attempt to quantify the rates of protein sequence divergence in Drosophila, we have devised a screen to differentiate between slow and fast evolving genes. We find that over one-third of randomly drawn cDNAs from a Drosophila melanogaster library do not cross-hybridize with Drosophila virilis DNA, indicating that they evolve with a very high rate. To determine the evolutionary characteristics of such protein sequences, we sequenced their homologs from a more closely related species (Drosophila yakuba). The amino acid substitution rates among these cDNAs are among the fastest known and several are only about 2-fold lower than the corresponding values for silent substitutions. An analysis of within-species polymorphisms for one of these sequences reveals an exceptionally high number of polymorphic amino acid positions, indicating that the protein is not under strong negative selection. We conclude that the Drosophila genome harbors a substantial proportion of genes with a very high divergence rate.
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Sequence comparisons of genomes or expressed sequence tags (ESTs) from related organisms provide insight into functional conservation and diversification. We compare the sequences of ESTs from the male accessory gland of Drosophila simulans to their orthologs in its close relative Drosophila melanogaster, and demonstrate rapid divergence of many of these reproductive genes. Nineteen (∼11%) of 176 independent genes identified in the EST screen contain protein-coding regions with an excess of nonsynonymous over synonymous changes, suggesting that their divergence has been accelerated by positive Darwinian selection. Genes that encode putative accessory gland-specific seminal fluid proteins had a significantly elevated level of nonsynonymous substitution relative to nonaccessory gland-specific genes. With the 57 new accessory gland genes reported here, we predict that ∼90% of the male accessory gland genes have been identified. The evolutionary EST approach applied here to identify putative targets of adaptive evolution is readily applicable to other tissues and organisms.
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We have examined the transport of the precursor of the 17-kD subunit of the photosynthetic O2-evolving complex (OE17) in intact chloroplasts in the presence of inhibitors that block two protein-translocation pathways in the thylakoid membrane. This precursor uses the transmembrane pH gradient-dependent pathway into the thylakoid lumen, and its transport across the thylakoid membrane is thought to be independent of ATP and the chloroplast SecA homolog, cpSecA. We unexpectedly found that azide, widely considered to be an inhibitor of cpSecA, had a profound effect on the targeting of the photosynthetic OE17 to the thylakoid lumen. By itself, azide caused a significant fraction of mature OE17 to accumulate in the stroma of intact chloroplasts. When added in conjunction with the protonophore nigericin, azide caused the maturation of a fraction of the stromal intermediate form of OE17, and this mature protein was found only in the stroma. Our data suggest that OE17 may use the sec-dependent pathway, especially when the transmembrane pH gradient-dependent pathway is inhibited. Under certain conditions, OE17 may be inserted across the thylakoid membrane far enough to allow removal of the transit peptide, but then may slip back out of the translocation machinery into the stromal compartment.
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The Mn K-edge x-ray absorption spectra for the pure S states of the tetranuclear Mn cluster of the oxygen-evolving complex of photosystem II during flash-induced S-state cycling have been determined. The relative S-state populations in samples given 0, 1, 2, 3, 4, or 5 flashes were determined from fitting the flash-induced electron paramagnetic resonance (EPR) multiline signal oscillation pattern to the Kok model. The edge spectra of samples given 0, 1, 2, or 3 flashes were combined with EPR information to calculate the pure S-state edge spectra. The edge positions (defined as the zero-crossing of the second derivatives) are 6550.1, 6551.7, 6553.5, and 6553.8 eV for S0, S1, S2, and S3, respectively. In addition to the shift in edge position, the S0--> S1 and S1--> S2 transitions are accompanied by characteristic changes in the shape of the edge, both indicative of Mn oxidation. The edge position shifts very little (0.3 eV) for the S2--> S3 transition, and the edge shape shows only subtle changes. We conclude that probably no direct Mn oxidation is involved in this transition. The proposed Mn oxidation state assignments are as follows: S0 (II, III, IV, IV) or (III, III, III, IV), S1 (III, III, IV, IV), S2 (III, IV, IV, IV), S3 (III, IV, IV, IV).
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The Camposanto of Pisa is an extraordinarily complex and evocative monument, which has captured the imagination of pilgrims, both religious and secular, for centuries. The late Medieval and early Renaissance wall paintings that line the perimeter of the portico surrounding a vast inner courtyard, are unparalleled in early Italian art, not only for their striking variety of composition and narrative complexity, but also for the sheer grandeur of their proportion. However, the passage of time has scarred the structure of the Camposanto and inflicted terrible damage on its wall paintings. This thesis explores the material reality of the Camposanto as experienced over three centuries through the eyes of British travelers. In order to situate the Camposanto mural cycle within an historical and cultural context, the first chapter provides an overview of the construction and decoration of the monument. Notably, Giorgio Vasari (1511-1574), the Italian Humanist often recognized as the father of art history, included numerous descriptions of the Camposanto murals in his highly influential text Vite de' più eccellenti pittori, scultori, ed architettori. Accordingly, the second chapter provides an analysis of Vasari’s descriptions and reflects upon the influence that the Renaissance author may have had upon the subsequent British reception of the Camposanto murals. The third chapter utilizes three centuries of travel writing in order to investigate the aesthetic impact of the Camposanto mural cycle upon British tourists from the seventeenth through to the nineteenth century.
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East Asian economic integration is less well known in Europe than is desirable in the EU’s own enlightened self-interest. It is also badly understood, not least because a range of ‘soft’ cultural, historical and political aspects are insufficiently appreciated in Europe. This CEPS Essay offers a deeper personal reflection on the emergence and development of East Asian economic cooperation and market-driven integration. It attempts to address some of the lingering reservations on both sides and to render the reservations in East Asia more intelligible to Europeans.
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After years of unchallenged commercial domination of a sizeable portion of the EU's gas market, Gazprom is confronted with a statement of objections issued on 22 April by the EU Commission for abusing its dominant market position. The company was already prevented from going ahead with its South Stream project aimed at consolidating Gazprom's grip on Southeast Europe's markets by bypassing Ukraine – due to alleged non-compliance of intergovernmental agreements with the EU regulatory framework. Furthermore, it walked away from negotiations that could have allowed it to access more than 50% of the OPAL pipeline – an onshore branch of the offshore Russian German Nord Stream pipeline –, whilst its attempts to go downstream through the acquisition of European distribution and transmission operators, such as Wingas and DESFA, failed due to current political tensions and the risk of a negative Commission ruling on the operation. Does this mean that the Russian gas behemoth – so often portrayed as the energy arm of the Kremlin – is not so powerful after all? This Policy Brief aims to frame the erosion of Gazprom's power in a wider perspective, analysing its peculiar position at a time of transition, with the global gas business going from a sellers' to a buyers' market, and providing recommendations on how Europe should deal with it. It will be argued that Gazprom – despite still being affected by the Kremlin's political priorities – is moving towards more commercially sound behavior. The EU should profit from this evolution without being tempted by mercantilist options, and rather use the political momentum provided by the energy union to remove barriers to solidarity and to increase competition on the trading platforms.
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Catharina Sørensen observes in this new EPIN Commentary that the most significant result of the Danish elections on June 18th was not the change of government from centre-left to centre-right, but rather the possibility that the anti-immigration, anti-European integration Danish People’s Party (DPP) would also enter government. While its leadership elected not to do so, but rather to exercise influence from outside, the author further notes that one positive outcome of a new pro-European government that is dependent on a largely eurosceptic supporting party could be that EU issues will finally get the prominence in Danish politics that they deserve.
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National Highway Traffic Safety Administration, Washington, D.C.
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Mode of access: Internet.
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Mode of access: Internet.
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"GAO/HEHS-00-20."