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71.
Identifying regions of the Drosophila melanogaster genome that have been recent targets of positive Darwinian selection will provide evidence for adaptations that have helped this species to colonize temperate habitats. We have begun a search for such genomic regions by analyzing multiple loci (about 250) dispersed across the X chromosome in a putatively ancestral population from East Africa and a derived European population. For both populations we found evidence for past changes in population size. We estimated that a major bottleneck associated with the colonization of Europe occurred about 3,500-16,000 years ago. We also found that while this bottleneck can account for most of the reduction in variation observed in the European sample, there is a deficit of polymorphism in some genomic regions that cannot be explained by demography alone. 相似文献
72.
Hooker SK Miller PJ Johnson MP Cox OP Boyd IL 《Proceedings. Biological sciences / The Royal Society》2005,272(1561):355-363
Novel observations collected from video, acoustic and conductivity sensors showed that Antarctic fur seals consistently exhale during the last 50-85% of ascent from all dives (10-160 m, n > 8000 dives from 50 seals). The depth of initial bubble emission was best predicted by maximum dive depth, suggesting an underlying physical mechanism. Bubble sound intensity recorded from one seal followed predictions of a simple model based on venting expanding lung air with decreasing pressure. Comparison of air release between dives, together with lack of variation in intensity of thrusting movement during initial descent regardless of ultimate dive depth, suggested that inhaled diving lung volume was constant for all dives. The thrusting intensity in the final phase of ascent was greater for dives in which ascent exhalation began at a greater depth, suggesting an energetic cost to this behaviour, probably as a result of loss of buoyancy from reduced lung volume. These results suggest that fur seals descend with full lung air stores, and thus face the physiological consequences of pressure at depth. We suggest that these regular and predictable ascent exhalations could function to reduce the potential for a precipitous drop in blood oxygen that would result in shallow-water blackout. 相似文献
73.
74.
Bulik S Peters B Holzhütter HG 《Journal of immunology (Baltimore, Md. : 1950)》2005,175(12):7957-7964
Antigenic peptides (epitopes) presented on the cell surface by MHC class I molecules derive from proteolytic degradation of endogenous proteins. Some recent studies have proposed that the majority of epitopes stem from so-called defective ribosomal products (DRiPs), i.e., freshly synthesized proteins that are unable to adopt the native conformation and thus undergo immediate degradation. However, a reliable computational analysis of the data underlying this hypothesis was lacking so far. Therefore, we have applied kinetic modeling to derive from existing kinetic data (Princiotta et al. 2003, Immunity 18, 343-354) the rates of the major processes involved in the cellular protein turnover and MHC class I-mediated Ag presentation. From our modeling approach, we conclude that in these experiments 1) the relative share of DRiPs in the total protein synthesis amounted to approximately 10% thus being much lower than reported so far, 2) DRiPs may become the decisive source of epitopes within an early phase after onset of the synthesis of a long-lived (e.g., virus derived) protein, and 3) inhibition of protein synthesis by the translation inhibitor cycloheximide appears to be paralleled with an instantaneous decrease of protein degradation down to approximately 1/3 of the normal value. 相似文献
75.
Matrix-assisted laser desorption-ionization (MALDI) mass spectrometry has evolved as a powerful method for analyzing nucleic acids. Here we provide protocols for genotyping single-nucleotide polymorphisms (SNPs) by MALDI based on PCR and primer extension to generate allele-specific products. Furthermore, we present three different approaches for sample preparation of primer-extension products before MALDI analysis and discuss their potential areas of application. The first approach, the 'GOOD' assay, is a purification-free procedure that uses DNA-modification chemistry, including alkylation of phosphorothioate linkages in the extension primers. The other two approaches use either solid-phase extraction or microarray purification for the purification of primer-extension products. Depending on the reaction steps of the various approaches, the protocols take about 6-8 hours. 相似文献
76.
Sascha Wohnsland Heinrich F. Bürgers Wolfgang Kuschinsky Martin H. Maurer 《Neurochemical research》2010,35(10):1635-1642
Several questions concerning the survival of isolated neurons and neuronal stem and progenitor cells (NPCs) have not been answered in the past: (1) If lactate is discussed as a major physiological substrate of neurons, do neurons and NPCs survive in a glucose-free lactate environment? (2) If elevated levels of glucose are detrimental to neuronal survival during ischemia, do high concentrations of glucose (up to 40 mmol/L) damage neurons and NPCs? (3) Which is the detrimental factor in oxygen glucose deprivation (OGD), lack of oxygen, lack of glucose, or the combination of both? Therefore, in the present study, we exposed rat cortical neurons and NPCs to different concentrations of d-glucose ranging from 0 to 40 mmol/L, or 10 and 20 mmol/L l-lactate under normoxic and anoxic conditions, as well as in OGD. After 24 h, we measured cellular viability by biochemical assays and automated cytochemical morphometry, pH values, bicarbonate, lactate and glucose concentrations in the cell culture media, and caspases activities. We found that (1) neurons and NPCs survived in a glucose-free lactate environment at least up to 24 h, (2) high glucose concentrations >5 mmol/L had no effect on cell viability, and (3) cell viability was reduced in normoxic glucose deprivation to 50% compared to 10 mmol/L glucose, whereas cell viability in OGD did not differ from that in anoxia with lactate which reduced cell viability to 30%. Total caspases activities were increased in the anoxic glucose groups only. Our data indicate that (1) neurons and NPCs can survive with lactate as exclusive metabolic substrate, (2) the viability of isolated neurons and NPCs is not impaired by high glucose concentrations during normoxia or anoxia, and (3) in OGD, low glucose concentrations, but not low oxygen levels are detrimental for neurons and NPCs. 相似文献
77.
CloQ is an aromatic prenyltransferase from the clorobiocin biosynthetic pathway of Streptomyces roseochromogenes var. oscitans. It is involved in the synthesis of the prenylated hydroxybenzoate moiety of the antibiotic, specifically catalyzing the attachment of a dimethylallyl moiety to 4-hydroxyphenylpyruvate. Herein, we report the crystal structure of CloQ and use it as a framework for interpreting biochemical data from both wild-type and variant proteins. CloQ belongs to the aromatic prenyltransferase family, which is characterized by an unusual core fold comprising five consecutive ααββ elements that form a central 10-stranded anti-parallel β-barrel. The latter delineates a solvent-accessible cavity where substrates bind and catalysis takes place. This cavity has well-defined polar and nonpolar regions, which have distinct roles in substrate binding and facilitate a Friedel-Crafts-type mechanism. We propose that the juxtaposition of five positively charged residues in the polar region circumvents the necessity for a Mg2+, which, by contrast, is a strict requirement for the majority of prenyltransferases characterized to date. Our structure of CloQ complexed with 4-hydroxyphenylpyruvate reveals the formation of a covalent link between the substrate and Cys215 to yield a thiohemiketal species. Through site-directed mutagenesis, we show that this link is not essential for enzyme activity in vitro. Furthermore, we demonstrate that CloQ will accept alternative substrates and, therefore, has the capacity to generate a range of prenylated compounds. Since prenylation is thought to enhance the bioactivity of many natural products, CloQ offers considerable promise as a biocatalyst for the chemoenzymatic synthesis of novel compounds with therapeutic potential. 相似文献
78.
Arabidopsis SPA proteins regulate photoperiodic flowering and interact with the floral inducer CONSTANS to regulate its stability 总被引:9,自引:0,他引:9
79.
Kurdyukov S Faust A Trenkamp S Bär S Franke R Efremova N Tietjen K Schreiber L Saedler H Yephremov A 《Planta》2006,224(2):315-329
In plants, extracellular matrix polymers built from polysaccharides and cuticular lipids have structural and protective functions. The cuticle is found to be ten times thinner in Arabidopsis thaliana (L.) Heynh than in many other plants, and there is evidence that it is unusual in having a high content of α-,ω-dicarboxylic fatty acids (FAs) in its polyesters. We designated the new organ fusion mutant hth-12 after it appeared to be allelic to adhesion of calyx edges (ace) and hothead (hth), upon molecular cloning of the gene by transposon tagging. This mutant is deficient in its ability to oxidize long-chain ω-hydroxy FAs to ω-oxo FAs, which results in leaf polyesters in decreased α-,ω-dicarboxylic FAs and increased ω-hydroxy FAs. These chemical phenotypes lead to disorder of the cuticle membrane structure in hth-12. ACE/HTH is a single-domain protein showing sequence similarity to long-chain FA ω-alcohol dehydrogenases from Candida species, and we hypothesize that it may catalyze the next step after cytochrome P450 FA ω-hydroxylases in the ω-oxidation pathway. We show that ACE/HTH is specifically expressed in epidermal cells. It appears very likely therefore that the changes in the amount of α-,ω-dicarboxylic FAs in hth-12 reflect the different composition of cuticular polyesters. The ACE/HTH gene is also expressed in root epidermal cells which do not form a polyester membrane on the exterior surface, thereby making it possible that the end products of the pathway, α-,ω-dicarboxylic FAs, are generally required for the cross-linking that ensures the integrity of the outer epidermal cell wall. 相似文献
80.