86 research outputs found
Regulatory competition in European company law
No full textRegulatory competition, European company law, Race to the top, Race to the bottom, Conflict of laws, Incorporation theory, Real seat theory, K29, K22,
Deoxyribozymes for peptide substrates: exploring the landscape of nucleophiles and electrophiles
No full textWhile DNA is most familiar in its double-stranded form as a storehouse of genetic information, its chemical similarities to naturally occurring ribozymes suggest that it can act as a catalyst. Single-stranded DNA molecules that have the ability to catalyze various bioorganic reactions are called deoxyribozymes. Deoxyribozymes do not occur naturally and are identified using a combinatorial chemistry technique called in vitro selection.
Since the discovery of the first artificial deoxyribozyme that catalyzes cleavage of phosphodiester bonds in RNA molecules, a number of deoxyribozymes have been identified that catalyze different bioorganic reactions, including RNA ligation, DNA phosphorylation, DNA deglycosylation, etc. Most of these reactions involve RNA or DNA substrates, where catalysis is facilitated by Watson-Crick base pairing between the substrate and the DNA catalyst. A major challenge in the field is to identify deoxyribozymes that can catalyze reactions involving non-nucleic acid substrates, such as proteins and sugars.
Addressing this challenge, we investigated the ability of DNA to catalyze reactions between amino acids that have nucleophilic side chains, such as tyrosine, serine, and lysine with a 5′-triphosphate-RNA electrophile. Previous efforts from our lab revealed DNA-catalyzed tyrosine reactivity, whereas serine proved refractory to catalysis. In the research described in Chapter 3, we identified for the first time, novel DNA enzymes that catalyze chemical modification of serine side chains. These deoxyribozymes were identified in a structurally preorganized three-helix-junction (3HJ) architecture that places the peptide nucleophile close to the triphosphate-RNA electrophile. We showed that these deoxyribozymes can discriminate between Ser and Tyr when presented at the same amino acid position and can also distinguish between multiple Ser side chains at different positions in the peptide. In studies performed in parallel, our results indicated that obtaining DNA-catalyzed Lys side chain reactivity is relatively difficult. Selection experiments with lysine substrate led to deoxyribozymes that catalyze reaction of a phosphoramidite functional group instead of the Lys side chain.
To address the difficulties in obtaining deoxyribozymes for Lys side chain reactions, we explored the ability of DNA to catalyze the reaction of amines with a more reactive electrophile, 2′,3′-cyclic phosphate as described in Chapter 4. However, multiple selection efforts involving the 2′,3′-cyclic phosphate electrophile, deoxyribozymes that catalyze a side reaction involving the ribose 2′-hydroxyl emerged. This study highlights some of the limitations of deoxyribozymes and the challenges associated with identifying deoxyribozymes that catalyze reactions involving amine nucleophiles.
We also sought to identify deoxyribozymes that can covalently tag phosphopeptides with RNA. These studies are described in Chapter 5. Such deoxyribozymes can be employed as reagents to isolate phosphopeptides from a mixture of peptides. We identified DNA enzymes that catalyze the nucleophilic attack of the phosphate group present in phosphotyrosine- and phosphoserine-containing peptides on 5′-triphosphate-RNA. These deoxyribozymes showed greater than 200-fold selectivity for phosphorylated peptides over non-phosphorylated analogs. The catalytic efficiency of one of these deoxyribozyme was assayed with a wide range of peptide substrates that differ in the identity of amino acid flanking the phosphorylated tyrosine. This deoxyribozyme catalyzes the reaction of these peptide sequences with similar catalytic efficiency.
Finally, as described in Chapter 6, we investigated the ability of DNA to catalyze phosphorylation of tyrosine and serine hydroxyls, that may be employed as artificial kinases. Artificial kinases could modulate numerous metabolic processes where naturally occurring kinases play an important role. In our first effort to identify kinase deoxyribozymes, we employed 5′-thiotriphosphate-RNA or GTPS as a phosphate donor. However, these selection experiments were unsuccessful, and we later identified that this was due to the instability of the thiotriphosphate moiety under the selection conditions. We then developed a novel selection approach that eliminated the use of thiotriphosphates. In this approach, capture deoxyribozymes that can attach an RNA molecule to phosphorylated peptides were employed to identify kinase deoxyribozymes. In these experiments the observed activity was found to depend on the covalent connection between the substrate and the DNA pool.Item withdrawn by Mark Zulauf ([email protected]) on 2011-09-12T15:00:32Z
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Agricultural trade liberalization in the Uruguay Round : one step forward, one step back?
No full textAfter evaluating the Uruguay Round's impact on agriculture and border protection in the next decade, the author concludes that while there was significant reform of the rules - particularly the conversion of nontariff barriers into tariffs and the reduction and binding of all tariffs - in practice, trade will probably be liberalized less than expected. The objective of the Round was to reverse protectionism and remove trade distortions. This may not be achieved in practice, at least not until further reductions are carried out in future rounds of negotiations. The major exception to this conclusion is in high-income Asian countries, where protection for major commodities will be significantly reduced. The tariffication and binding of all tariffs on agricultural products represents a significant step forward. Liberalization is implicit because countries are prohhibited from arbitrarily raising tariffs to new higher levels. But many of the newly established tariffs are so high in many countries as to effectively prohibit trade. Patterns of liberalization vary considerably by commodity and by country. Generally, the extent of liberalization was diminished by binding tariffs to the base period of 1986-88, when border protection was at a high point. In most OECD countries, this was worsened by"dirty tariffication:"the new base tariffs offered even greater protection than the nontariff barriers they replaced. Even after the commitments to tariff reductions in the Round, the ad valorem measure of the final binding tariffs will remain higher than the average rate of protection in 1982-93. A number of developing countries in East Asia, Latin America, and the Middle East chose to lock in prior liberalization efforts on some products. But for most commodities, there will be little actual liberalization, since most developing countries chose to bind their tariffs at a maximum level. Even when countries reduced already-bound rates, bound tariffs remained significantly higher than current applied rates, giving countries the flexibility to raise tariffs later. The high level of bound tariffs may allow countries to apply variable tariffs below the bound level, thus failing to stabilize tariffs and improve market access. Moreover, the Round did not touch many of the worst distortions in developing countries, such as import subsidies, export taxes, state-trading monopolies, and domestic policies that implicitly tax agriculture.Trade Policy,Environmental Economics&Policies,Economic Theory&Research,Export Competitiveness,Rules of Origin,Trade Policy,Rules of Origin,TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Environmental Economics&Policies,Economic Theory&Research
Effect of the optimisation time interval on the performance of mobile networks
No full textThis thesis project researches the effect of the optimisation time interval on the performance of a self-optimised mobile network. The goal of the thesis is to ascertain if there exists an optimal time interval for the self-optimisation of the KPN network, and what that interval is. In order to research this question, the project uses data from the KPN network as input, and sets up a simulation study in MATLAB. Two areas in the Netherlands are considered in this study – Friesland and Purmerend. The self-optimisation of the network is carried out through the modification of three optimisation parameters – antenna tilt, RS power, and Cell Individual Offset. The scope of the study is limited to LTE in the downlink, for the 800 MHz band. The bandwidth used in this study is 10 MHz. The performance of the mobile network has been studied using KPIs such as 10th throughput percentile, coverage failure rate, call drop rate, and load. In the end, the study analyses the results for each area, for the self-optimisation carried out by modifying the three parameters over several different optimisation time intervals, and discusses their impact on the performance of the network. A comparison has also been drawn between the performance of a self-optimised network and an un-optimised network, to highlight the gains achieved with SON. Finally, recommendations are made regarding a suitable time interval, and a relative comparison between suitability of the three optimisation parameters has been drawn. The study finds that a suitable time interval for optimisation does exist, and is 240 minutes, for both the simulation areas. The study finds RS power to be the most suitable parameter for self-optimisation, in both the areas. However, the research runs into some unexpected results with respect to the optimisations using tilt angle, and has been discussed in detail in the report. Significant gains are observed with SON, as compared to the case of ‘No SON’ or an un-optimised network. Electrical Engineering | Network Architectures and Service
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