Showing papers by "University of Luxembourg published in 1994"

Correlated mutations and residue contacts in proteins.

Abstract: The maintenance of protein function and structure constrains the evolution of amino acid sequences. This fact can be exploited to interpret correlated mutations observed in a sequence family as an indication of probable physical contact in three dimensions. Here we present a simple and general method to analyze correlations in mutational behavior between different positions in a multiple sequence alignment. We then use these correlations to predict contact maps for each of 11 protein families and compare the result with the contacts determined by crystallography. For the most strongly correlated residue pairs predicted to be in contact, the prediction accuracy ranges from 37 to 68% and the improvement ratio relative to a random prediction from 1.4 to 5.1. Predicted contact maps can be used as input for the calculation of protein tertiary structure, either from sequence information alone or in combination with experimental information.

On the Biasedness of Forward Foreign Exchange Rates: Irrationality or Risk Premia?

Abstract: In this article we reconsider the Foot and Frankel results on the sources of forward discount bias. We question the economic validity of some estimation restrictions that they impose and, thus, are led to question some of their results. We employ a new exchange rate survey database that includes European Monetary System currencies and use univariate and pooling estimation techniques that impose fewer restrictions than those of Froot and Frankel to test our hypotheses. We find that the bias in the forward discount to BOTH (author emphasis) the failure of rational expectations and the existence of time-varying risk premia.

Functional differences between L- and T-plastin isoforms.

Abstract: Fimbrins/plastins are a family of highly conserved actin-bundling proteins They are present in all eukaryotic cells including yeast, but each isoform displays a remarkable tissue specificity T-plastin is normally found in epithelial and mesenchymal cells while L-plastin is present in hematopoietic cells However, L-plastin has been also found in tumor cells of non-hematopoietic origin (Lin, C-S, R H Aebersold, S B Kent, M Varma, and J Leavitt 1988 Mol Cell Biol 8:4659-4668; Lin, C-S, R H Aebersold, and J Leavitt 1990 Mol Cell Biol 10: 1818-1821) To learn more about the biological significance of their tissue specificity, we have overproduced the T- and L-plastin isoforms in a fibroblast-like cell line, CV-1, and in a polarized epithelial cell line, LLC-PK1 In CV-1 cells, overproduction of T- and L-plastins induces cell rounding and a concomitant reorganization of actin stress fibers into geodesic structures L-plastin remains associated with microfilaments while T-plastin is almost completely extracted after treatment of the cells with non-ionic detergent In LLC-PK1 cells, T-plastin induces shape changes in microvilli and remains associated with microvillar actin filaments after detergent extraction while L-plastin has no effect on these structures and is completely extracted The effect of T-plastin on the organization of microvilli differs from that of villin, another actin-bundling protein Our experiments indicate that these two isoforms play differing roles in actin filament organization, and do so in a cell type-specific fashion Thus it is likely that these plastin isoforms play fundamentally different roles in cell function

Differentiation-specific isoform mRNA expression of the calmodulin-dependent plasma membrane Ca(2+)-ATPase.

Abstract: The functional significance of the isoform diversity of the calmodulin-dependent plasma membrane Ca(2+)-ATPase (PMCA) is largely unknown. To determine whether the mRNA synthesis of different isoforms of the enzyme is regulated in a differentiation-specific manner, we investigated the expression of isoform-specific mRNAs in muscle and neuronal cells during differentiation by reverse transcription PCR. In the rat, the ubiquitous PMCA splicing variants 1b and 4b formed the typical PMCA isoform pattern of L6 myoblasts, the heart-derived cell line H9c2(2-1), two different fibroblast cell lines (FR and NRK-49F), smooth muscle, and endothelial cells. In addition to these two enzymes, novel expression of the splicing variants 1c, 1d, and 4a was induced during myogenic differentiation of L6 and H9c2(2-1) cells. A similar isoform subtype switch could be detected during differentiation of the neuronal PC-12 cells induced by nerve growth factor (NGF). The isoform-specific mRNAs 1c, 1d, and 4a were not expressed in ce...

Effects of nisoldipine on endothelin-1- and angiotensin II-induced immediate/early gene expression and protein synthesis in adult rat ventricular cardiomyocytes.

Abstract: The cellular mechanisms by which dihydropyridine-type calcium antagonists lead to regression of hypertension-related cardiac hypertrophy have not been clarified. We previously showed that angiotensin II (AII) and endothelin-1 (ET-1) induce protein synthesis in isolated adult rat cardiomyocytes, probably through protein kinase C (PKC) as second messenger and the gene product of the early growth response gene-1 (Egr-1) as third messenger. We now show that the dihydropyridine derivative nisoldipine inhibits AII- and ET-1-induced protein synthesis at low concentrations (IC50 7.5 nM for 0.1 microM ET). Induction of c-fos and Egr-1 mRNA by AII and ET was completely blocked by nisoldipine. Therefore, nisoldipine may influence the signal transduction pathway, i.e., through PKC. These results provide a potential pressure-independent mechanism by which nisoldipine may influence development of cardiac hypertrophy.

The Dynamics of Short-term Interest Rate Volatility Reconsidered

Abstract: In this paper we present and estimate a model of short-term interest rate volatility, that encompasses both the level effect of Chan, Karolyi, Longstaff and Sanders (1992) and the conditional heteroskedasticity effect of the GARCH class of models. This flexible specification allows different effects to dominate as the level of the interest rate varies. We also investigate implications for the pricing of discount bond options. Our findings indicate that the inclusion of a volatility effect in addition to a level effect in the model specification is particularly relevant for the pricing of shorter-term discount bond options.

Evolution and Neural Networks – Protein Secondary Structure Prediction Above 71% Accuracy

Abstract: Some 30,Wprotein sequences are known. For 1,000 the structure is experimentally solved. Another 4,000 can be modeled by homology. For the remaining 25,000 sequences, the tertiary structure (30) cannot be predicted generally from the sequence. A reduction of the problem is the projection of 30 structure onto a one-dimensional string of secondary structure assignments. Predictions in three states rate between 36% (random) and 88% (homology modelling) accuracy. Here, we present an improvement of a neural network system using informalion about evolutionary conservation. The method achieves a sustained overall accuracy of 71.4%. A test on 45 new proteins confirms the estimated accuracy. Of practical importance is the definition of a reliability index at each residue position: e.g. about 40% of the predicted residues have an expected accuracy of 88%. The method has been made publicly available by an automatic e-mail server.

Relations between different approaches to the relativistic two-body problem

Abstract: The relativistic and quantum mechanical two-body problem with interaction has been a controversial matter for many decades. We show that two very different approaches to the problem for a particular type of interaction lead to the same final equation. Furthermore, the second of them can be solved exactly in an elementary fashion, and leads to an equally spaced spectrum of a familiar type for the square of the total energy.

Mapping and load balancing on distributed memory systems

Abstract: Two kinds of tools are necessary to optimise the use of available resources by the execution of parallel programs on distributed memory systems: mapping and load balancing tools. A mapping tool is well suited for programs whose behaviour is predictable while for many "real applications", it needs to be complemented by a dynamic load balancing tool. Both tools are currently investigated to be included in the programming environment designed by the SEPP COPERNICUS project.

Stochastic Trends and Jumps In EMS Exchange Rates

Abstract: In this paper we study the statistical properties of EMS exchange rate returns. Our findings show that jumps, time- varying parameters, and conditional leptokurtosis are pertinent features in the empirical distributions of EMS exchange rate returns. Allowance for fat tails, however, tends to reduce the measured frequency of jumps in the distributions to more realistic proportions. Most successful in capturing the relevant features of EMS exchange rate returns is a combined jump-GARCH model with conditionally t-distributed innovations.