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981.
Moore RB Oborník M Janouskovec J Chrudimský T Vancová M Green DH Wright SW Davies NW Bolch CJ Heimann K Slapeta J Hoegh-Guldberg O Logsdon JM Carter DA 《Nature》2008,451(7181):959-963
Many parasitic Apicomplexa, such as Plasmodium falciparum, contain an unpigmented chloroplast remnant termed the apicoplast, which is a target for malaria treatment. However, no close relative of apicomplexans with a functional photosynthetic plastid has yet been described. Here we describe a newly cultured organism that has ultrastructural features typical for alveolates, is phylogenetically related to apicomplexans, and contains a photosynthetic plastid. The plastid is surrounded by four membranes, is pigmented by chlorophyll a, and uses the codon UGA to encode tryptophan in the psbA gene. This genetic feature has been found only in coccidian apicoplasts and various mitochondria. The UGA-Trp codon and phylogenies of plastid and nuclear ribosomal RNA genes indicate that the organism is the closest known photosynthetic relative to apicomplexan parasites and that its plastid shares an origin with the apicoplasts. The discovery of this organism provides a powerful model with which to study the evolution of parasitism in Apicomplexa. 相似文献
982.
The first hominin of Europe 总被引:3,自引:0,他引:3
Carbonell E Bermúdez de Castro JM Parés JM Pérez-González A Cuenca-Bescós G Ollé A Mosquera M Huguet R van der Made J Rosas A Sala R Vallverdú J García N Granger DE Martinón-Torres M Rodríguez XP Stock GM Vergès JM Allué E Burjachs F Cáceres I Canals A Benito A Díez C Lozano M Mateos A Navazo M Rodríguez J Rosell J Arsuaga JL 《Nature》2008,452(7186):465-469
The earliest hominin occupation of Europe is one of the most debated topics in palaeoanthropology. However, the purportedly oldest of the Early Pleistocene sites in Eurasia lack precise age control and contain stone tools rather than human fossil remains. Here we report the discovery of a human mandible associated with an assemblage of Mode 1 lithic tools and faunal remains bearing traces of hominin processing, in stratigraphic level TE9 at the site of the Sima del Elefante, Atapuerca, Spain. Level TE9 has been dated to the Early Pleistocene (approximately 1.2-1.1 Myr), based on a combination of palaeomagnetism, cosmogenic nuclides and biostratigraphy. The Sima del Elefante site thus emerges as the oldest, most accurately dated record of human occupation in Europe, to our knowledge. The study of the human mandible suggests that the first settlement of Western Europe could be related to an early demographic expansion out of Africa. The new evidence, with previous findings in other Atapuerca sites (level TD6 from Gran Dolina), also suggests that a speciation event occurred in this extreme area of the Eurasian continent during the Early Pleistocene, initiating the hominin lineage represented by the TE9 and TD6 hominins. 相似文献
983.
A semiotic theory of systems derived from language would have the purpose of classifying all the systems of linguistic expression: philosophy, ideology, myth, poetry, art, as much as the dream, lapsus, and free association in a pluridimensional matrix that will interact with many diversified fields. In each one of these discourses it is necessary to consider a plurality of questions, the essence of which will only be comprehensible by the totality; it will be necessary to ask, in the first place, what will be the purpose of this language, what function does it fulfill and for which reason has it been constructed. The concept of World vision (WV) is introduced and its relation with Generalized Collective Conscience (GCC) and Particularized Collective Conscience. Culture implies a particular WV. Culture creates GCC. The semantic field is a structure that formalizes the units of a certain culture constituting a portion of the vision of the Reality that owns this culture. An ecological case is explained. 相似文献
984.
Hepatitis C virus (HCV) translation is mediated by an internal ribosome entry site (IRES) located at the 5′ end of the genomic
RNA. The 3′ untranslatable region (3′UTR) stimulates translation by the recruitment of protein factors that simultaneously
bind to the 5′ end of the viral genome. This leads to the formation of a macromolecular complex with a closed loop conformation,
similar to that described for the cap-translated mRNAs. We previously demonstrated the existence of a long-range RNA–RNA interaction
involving subdomain IIId of the IRES region and the stem–loop 5BSL3.2 of the CRE element at the 3′ end of the viral genome.
The present study provides evidence that the enhancement of HCV IRES-dependent translation mediated by the 3′UTR is negatively
controlled by the CRE region in the human hepatoma cell lines Huh-7 and Hep-G2 in a time-dependent manner. Domain 5BSL3.2
is the major partner in this process. Mutations in this motif lead to an increase in IRES activity by up to eightfold. These
data support the existence of a functional high order structure in the HCV genome that involves two evolutionarily conserved
RNA elements, domain IIId in the IRES and stem–loop 5BSL3.2 in the CRE region. This interaction could have a role in the circularisation
of the viral genome. 相似文献
985.
Carlos A. López-González Robert W. Jones Carmen Silva-Hurtado Ivan A. Sáyago-Vázquez 《西北部美国博物学家》2011,69(1)
The remains of the scorpion Diplocentrus peloncillensis Francke were found in 7 scats of black bears ( Ursus americanus ) collected in the Sierra de San Luis, Sonora, Mexico. The collection data and previously reported black bear population estimates for the study area suggested that, although scorpions are not a large part of black bear diets in Sonora, feeding on scorpions is not restricted to a single individual or family unit and is apparently a relatively common behavior in the population. Also, the discovery of D. peloncillensis in Sonora represents a new country record. 相似文献
986.
Dryocoetes confusus Swaine, the western balsam bark beetle, is an important bark beetle associated with Abies lasiocarpa (Hook.) Nutt. (subalpine fir) in western North America. Little information is available on the life cycle and ecology of this insect in Colorado. In this study in north central Colorado, we examined its flight periodicity, attack patterns, and life cycle in downed trees. Flight season, as indicated by pheromone-trap catches, began in early June. Peak flight was observed during early to mid-July. A second peak in flight was observed in some years, but its occurrence was not consistent. Preferred attack sites on downed trees were the underside or side of the log and through branch stubs. The life cycle for this beetle was completed in 2 years, consistent with earlier observations from British Columbia. Sex ratio was 1:1, but a higher percentage of males fly earlier in the season. 相似文献
987.
Diola Marina Núñez-Ramírez Aquiles Solís-Soto Javier López-Miranda Benito Pereyra-Alférez Miriam Rutiaga-Quiñónes Luis Medina-Torres Hiram Medrano-Roldán 《矿物冶金与材料学报》2011,18(5):523-526
The iron concentrate from Hercules Mine of Coahuila, Mexico, which mainly contained pyrite and pyrrhotite, was treated by
the bioleaching process using native strain Acidithiobacillus ferrooxidans (A. ferrooxidans) to determine the ability of these bacteria on the leaching of zinc. The native bacteria were isolated from the iron concentrate
of the mine. The bioleaching experiments were carried out in shake flasks to analyze the effects of pH values, pulp density,
and the ferrous sulfate concentration on the bioleaching process. The results obtained by microbial kinetic analyses for the
evaluation of some aspects of zinc leaching show that the native bacteria A. ferrooxidans, which is enriched with a 9K Silverman medium under the optimum conditions of pH 2.0, 20 g/L pulp density, and 40 g/L FeSO4, increases the zinc extraction considerably observed by monitoring during15 d, i.e., the zinc concentration has a decrease of about 95% in the iron concentrate. 相似文献
988.
Maria J. Marcaida Inés G. Muñoz Francisco J. Blanco Jesús Prieto Guillermo Montoya 《Cellular and molecular life sciences : CMLS》2010,67(5):727-748
Homing endonucleases (HE) are double-stranded DNAses that target large recognition sites (12–40 bp). HE-encoding sequences
are usually embedded in either introns or inteins. Their recognition sites are extremely rare, with none or only a few of
these sites present in a mammalian-sized genome. However, these enzymes, unlike standard restriction endonucleases, tolerate
some sequence degeneracy within their recognition sequence. Several members of this enzyme family have been used as templates
to engineer tools to cleave DNA sequences that differ from their original wild-type targets. These custom HEs can be used
to stimulate double-strand break homologous recombination in cells, to induce the repair of defective genes with very low
toxicity levels. The use of tailored HEs opens up new possibilities for gene therapy in patients with monogenic diseases that
can be treated ex vivo. This review provides an overview of recent advances in this field. 相似文献
989.
This article reviews some major episodes in the history of the spatial isomorphism problem of dynamical systems theory (ergodic
theory). In particular, by analysing, both systematically and in historical context, a hitherto unpublished letter written
in 1941 by John von Neumann to Stanislaw Ulam, this article clarifies von Neumann’s contribution to discovering the relationship
between spatial isomorphism and spectral isomorphism. The main message of the article is that von Neumann’s argument described
in his letter to Ulam is the very first proof that spatial isomorphism and spectral isomorphism are not equivalent because
spectral isomorphism is weaker than spatial isomorphism: von Neumann shows that spectrally isomorphic ergodic dynamical systems
with mixed spectra need not be spatially isomorphic. 相似文献
990.
András Kertész 《Foundations of Science》2012,17(1):91-108
Chomsky’s principle of epistemological tolerance says that in theoretical linguistics contradictions between the data and
the hypotheses may be temporarily tolerated in order to protect the explanatory power of the theory. The paper raises the
following problem: What kinds of contradictions may be tolerated between the data and the hypotheses in theoretical linguistics?
First a model of paraconsistent logic is introduced which differentiates between week and strong contradiction. As a second
step, a case study is carried out which exemplifies that the principle of epistemological tolerance may be interpreted as
the tolerance of week contradiction. The third step of the argumentation focuses on another case study which exemplifies that
the principle of epistemological tolerance must not be interpreted as the tolerance of strong contradiction. The reason for
the latter insight is the unreliability and the uncertainty of introspective data. From this finding the author draws the
conclusion that it is the integration of different data types that may lead to the improvement of current theoretical linguistics
and that the integration of different data types requires a novel methodology which, for the time being, is not available. 相似文献