Characterisation of two alcohol acyltransferases from kiwifruit (Actinidia spp.) reveals distinct substrate preferences.

Volatile esters are key compounds of kiwifruit flavour and are formed by alcohol acyltransferases that belong to the BAHD acyltransferase superfamily. Quantitative RT-PCR was used to screen kiwifruitderived expressed sequence tags with proposed acyltransferase function in order to select ripeningspecific sequences and test their involvement in alcohol acylation. The screening criterion was for at least 10-fold increased transcript accumulation in ripe compared with unripe kiwifruit and in response to ethylene. Recombinant expression in yeast revealed alcohol acyltransferase activity for Actinidia-derived AT1, AT16 and the phylogenetically distinct AT9, using various alcohol and acyl-CoA substrates. Functional characterisation of AT16 and AT9 demonstrated striking differences in their substrate preferences and apparent catalytic efficiencies ðV0 max K�1 m Þ. Thus revealing benzoyl-CoA:alcohol O-acyltransferase activity for AT16 and acetyl-CoA:alcohol O-acyltransferase activity for AT9. Both kiwifruit-derived enzymes displayed higher reaction rates with butanol compared with ethanol, even though ethanol is the main alcohol in ripe fruit. Since ethyl acetate and ethyl benzoate are major esters in ripe kiwifruit, we suggest that fruit characteristic volatile profiles result from a combination of substrate availability and specificity of individual alcohol acyltransferases

Différenciation génétique de quelques populations de Chrysichthys nigrodigitatus et de C. johnelsi (Pisces, Bagridae) de Côte d'Ivoire et du Mali

Le polymorphisme de 19 locus codant pour des enzymes a été étudié dans six populations de #Chrysichthys nigrodigitatus Lacépède 1803 (#Pisces, Bagridae), espèce utilisée en aquaculture africaine, et une population de #Chrysischthys johnelsi Daget 1959. La population de #C. nigrodigitatus du bassin du Niger (Bamako, Mali) est nettement différenciée des populations des bassins du Sassandra, du Bandama, de la Comoé et des lagunes Ebrié et Aby en Côte d'Ivoire (0,233 <D<0,266). Etant donné la grande répartition géographique de #C. nigrodigitatus$qui s'étend de l'Angola au Sénégal, Ces résultats laissent penser que l'espèce présente une forte différenciation génétique que l'on pourrait mettre à profit dans un programme d'amélioration génétique en aquaculture. Les échantillons des lagunes Ebrié et Aby (Côte d'Ivoire) présentent des taux de polymorphisme les plus importants (H = 4,5$ présente également un polymorphisme et cette espèce, proche de #C. nigrodigitatus$, pourrait être utilisée pour obtenir des hybrides ou des lignées gynogénétiques. (Résumé d'auteur

The absolutely continuous spectrum of one-dimensional Schr"odinger operators

This paper deals with general structural properties of one-dimensional Schr"odinger operators with some absolutely continuous spectrum. The basic result says that the omega limit points of the potential under the shift map are reflectionless on the support of the absolutely continuous part of the spectral measure. This implies an Oracle Theorem for such potentials and Denisov-Rakhmanov type theorems. In the discrete case, for Jacobi operators, these issues were discussed in my recent paper [19]. The treatment of the continuous case in the present paper depends on the same basic ideas.Comment: references added; a few very minor change

Challenges in the development of effective systems for Professional Legal Search

The key objective of an information retrieval (IR) system is to identify and return to the user content relevant or useful in addressing the information need which required them to use the system. The development and evaluation of IR systems relies on the availability of suitable datasets or test collections. These typically consist of a target document collection, example search queries representative of those that users of the system to be developed, are expected to enter, and relevance data indicating which documents in the collection are relevant to the information needed as expressed in each query. Public research in IR has focused on popular content, e.g. news corpora or web content, for which average users can pose queries expressing information needs and judge the relevance of retrieved documents. This is not the case for professional search applications, for example legal, medical, financial search where domain experts are required for these tasks. We describe our experiences from the development of a professional legal IR application employing semantic search technologies. Our activities indicate the vital need for close interaction between the professionals for which the application is being developed and the IR researchers throughout the development life cycle of the search system. Such engagement is vital in order for the IR researchers to understand the working practices of the professional searchers, the specifications of their information needs and the domain in which they are searching, and to study how they engage and interact with information. A key reason to seek to understand these topics so deeply is to facilitate meaningful evaluation of the effectiveness of IR technologies as components in the system being developed