The zebrafish (Danio rerio) provides an excellent model for studying vertebrate development and human disease because of its ex utero, optically transparent embryogenesis and amenability to in vivo manipulation. The rapid embryonic developmental cycle, large clutch sizes and ease of maintenance at large numbers also add to the appeal of this species. Considerable genomic data has recently become publicly available that is aiding the construction of zebrafish microarrays, thus permitting global gene expression analysis. The zebrafish is also suitable for chemical genomics, in part as a result of the permeability of its embryos to small molecules and consequent avoidance of external confounding maternal effects. Finally, there is increasing characterization and analysis of zebrafish models of human disease. Thus, the zebrafish offers a high-quality, high-throughput bioassay tool for determining the biological effect of small molecules as well as for dissecting biological pathways.
Humans vary in their ability to smell numerous odors [1-3], including those associated with food [4-6]. Odor sensitivity is heritable [7-11], with examples linking genetic variation for sensitivity to specific odors typically located near olfactory receptor (OR) genes [12-16]. However, with thousands of aromas and few deorphaned ORs [17, 18], there has been little progress toward linking variation at OR loci to odor sensitivity [19, 20]. We hypothesized that OR genes contain the variation that explains much of the differences in sensitivity for odors, paralleling the genetics of taste [21, 22], which affect the flavor experience of foods [23-25]. We employed a genome-wide association approach for ten food-related odors and identified genetic associations to sensitivity for 2-heptanone (p = 5.1 × 10(-8)), isobutyraldehyde (p = 6.4 × 10(-10)), β-damascenone (p = 1.6 × 10(-7)), and β-ionone (p = 1.4 × 10(-31)). Each locus is located in/near distinct clusters of OR genes. These findings increase the number of olfactory sensitivity loci to nine and demonstrate the importance of OR-associated variation in sensory acuity for food-related odors. Analysis of genotype frequencies across human populations implies that variation in sensitivity for these odors is widespread. Furthermore, each participant possessed one of many possible combinations of sensitivities for these odors, supporting the notion that everyone experiences their own unique "flavor world."
The sequences of the 16s rRNA genes of 20 lltermus isolates were determined to a high fidelity by using automated DNA sequencing and fluorescent-dye-labelled primers. The strains tested included members of the three validly named Thennus species and representatives of major taxonomic clusters defined previously for this genus. The parsimony method was used to reconstruct the phylogeny of the strains from the aligned sequences, and a bootstrap analysis revealed a number of well-supported clades. Our results are not consistent with groupings inferred from numerical taxonomy data but support the conjecture that the genus Thennus contains more species than the three currently recognized species.Since the original description of the genus Thermus by Brock and Freeze (4), the ubiquitous nature of members of this taxon has been demonstrated by the ready isolation of strains from neutral-pH thermal areas around the world (reviewed in reference 48). The genus Thermus represents a deep eubacterial branch (16) and contains three validly named species: Thermus aquaticus (4), Thermus ruber (26), and Thermus filiformis (20). Many other Thermus isolates have been described in some detail but have not yet been validly named; the taxonomy of the genus is still incomplete. While there is general agreement that T. ruber and T. aquaticus are taxonomically and phylogenetically distinct (17), it is still unclear whether the yellow-pigmented isolates that grow at 70°C constitute a single species or more than one species. In a numerical taxonomic study Hudson et al. (21) discerned eight species groups which were separated at a simple matching coefficient value of 65%, while Williams (47) suggested that there are at least four genospecies on the basis of DNA-DNA hybridization data and other properties. In both cases there were strong indications that strains isolated from the same thermal region shared common properties and grouped together. A comparison of results is difficult because different strains have been used in different studies.In this study the sequences of the 16s rRNA genes of 20 Thermus strains were determined by using a procedure developed specifically to provide high-fidelity data with an automated DNA sequencer, and the aligned sequences were subjected to phylogenetic analysis. The complete 16s rRNA gene sequence of "Thermus thermophilus" HB8 (29) and a partial sequence of T. aquaticus (45) were available from other sources, but the results described below were derived from our own sequence versions. The 20 strains included representatives of the major clusters defined in the study of Hudson et al. (21) and the three validly named species, as well as two "T. thermophilus" strains (HB8 and HB27) and '' Thermus flavus . "Phylogenetic systematics is a two-stage process. The first stage is the estimation of a phylogenetic tree, and for this we used aligned sequence data and reconstructed the phylogeny by using the criterion of maximum parsimony (44). The * Corresponding author. second stage is the translation of the phyl...
Caldocellum saccharolyticum" is an obligatory anaerobic thermophilic bacterium. A gene from this organism, designated celB, has been cloned in Eschenichia coli as part of a bacteriophage A gene library. This gene produces a thermostable cellulase that shows both endoglucanase and exoglucanase activities on test substrates and is able to degrade crystalline cellulose to glucose. The sequence of celB has homology with both exo-and endoglucanases described by others. It appears to have a central domain without enzymatic activity which is joined to the enzymatic domains by runs of amino acids rich in proline and threonine (PT boxes). Deletion analysis shows that the exoglucanase activity is located in the amino-terminal domain of the enzyme and that endoglucanase activity is located in the carboxy-terminal domain. There are internal transcriptional and translational start sites within the gene. The intact gene has been cloned into a temperature-inducible expression vector, pJLA602, and overexpressed in E. coli. Polyacrylamide gel electrophoresis showed that celB produced a protein with a molecular weight of 118,000 to 120,000. A number of smaller proteins with activity against carboxymethyl cellulose and 4-methyl umbelliferyl-o-D-cellobioside were also produced. These are believed to be the result of alternative translational start sites and/or proteolytic degradation products of the translated gene product. The cellulase system comprises three general classes of enzymes: exoglucanases (P-1,4-D-glucan cellobiohydrolase), endoglucanases (P-1,4-D-glucan glucanhydrolase), and
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