Perceptual organization of onsets and offsets of sounds

Several illusory phenomena in auditory perception are accounted for by using the event construction model presented by Nakajima et al. (2000) in order to explain the gap transfer illusion. This model assumes that onsets and offsets of sounds are detected perceptually as if they were independent auditory elements. They are connected to one another according to the proximity principle to constitute auditory events. This model seems to contribute to a general cross-modal theory of perception where the idea of edge integration plays an important role. Potential directions in which we can connect the present paradigm with speech perception are indicated, and possibilities to improve artificial auditory environments are suggested.     

Molecular phylogenetic relationships of Eastern Asian Cyprinidae (Pisces: Cypriniformes) inferred from cytochrome b sequences

Cyprinidae, the largest fish family, comprises ap-proximately 210 recognized genera and 2010 species that are distributed widely in Eurasia, East Indian Is-land, Africa, and North America[1]. Species richness of this family is the greatest in East Asia, for example, China has 122 genera and more than 600 species. It is difficult to build a comprehensive phylogeny of Cy-prinidae due to the large number of genera and species. The classification of this family has been subject to revisions an…     

Nucleotide sequence of the p53 cDNA of beluga whale (Delphinapterus leucas)

The cDNA (DNA complementary to RNA) of the p53 gene of the beluga whale (Delphinapterus leucas) was sequenced by the method of 5'- and 3'-rapid amplification of cDNA ends (RACE) with the cDNA made for the RNA obtained from fresh peripheral blood leukocytes isolated from two animals. Primers for the RACE method were synthesized based on the sequence of the DNA of beluga whale corresponding to exon 5 of the human p53 gene, which was determined after amplification of the DNA isolated from the liver from a beluga whale by using a pair of primers for the human sequence. The sequenced cDNA had a 2150-nucleotide length and contained the whole region corresponding to human exons 1 through 11. The reading frame was 1164 bp (base pair) long and began in exon 2 and ended in exon 11, coding for a 387-amino acid protein. The nucleotide sequence of the reading frame showed high similarity over 85% with pig, sheep, cow, and human genes. The similarities with the former two animals at the amino acid level were also more than 85%. Lower similarity of the beluga whale p53 gene was also found with those of lower tetrapods, fish and invertebrates.     

A new polypeptide toxin from the nematocyst venom of an Okinawan sea anemone Phyllodiscus semoni (Japanese name "unbachi-isoginchaku")

The venomous sea anemone Phyllodiscus semoni causes cases of severe stinging. We isolated Phyllodiscus semoni toxin 20A (PsTX-20A), a hemolytic and lethal polypeptide (20 kDa), from the nematocyst venom of this species for the first time. Furthermore, we sequenced the cDNA encoding PsTX-20A. The deduced amino acid sequence of PsTX-20A showed that this toxin was a new member of the actinoporin family, which consists of several cytolytic polypeptides originating from sea anemones. PsTX-20A showed lethal toxicity to the shrimp Palaemon paucidens when administered via intraperitoneal injection (LD50, 50 microg/kg) and hemolytic activity toward 0.8% sheep red blood cells (ED50, 80 ng/ml).     

Cloning and expression of the exo-beta-D-1,3-glucanase gene (exgS) from Aspergillus saitoi

A gene of exo-1,3-beta-D-glucanase (exgS) was cloned from a koji mold, Aspergillus saitoi, genomic DNA using PCR. The exgS has an ORF comprising 2832 bp, which contains one intron of 45 bp, and encodes 945 amino acids. The deduced amino acid sequences showed that the ExgS has a non-homologous linker region consisting of 180 amino acids, which encompassed highly conserved regions observed in Exg homologues from filamentous fungi. A recombinant protein (ExgS) has been recovered from the cultural filtrate of an Aspergillus oryzae strain that carried an expression vector containing full length of the exgS. The N-terminal amino acid sequences of the recombinant exo-1,3-beta-D-glucanase (ExgS) were identical to that of native ExgS from A. saitoi.     

Spatial and temporal aspects of Ca2+ signaling mediated by P2Y receptors in cultured rat hippocampal astrocytes

ATP produces a variety of Ca2+ responses in astrocytes. To address the complex spatio-temporal Ca2+ signals, we analyzed the ATP-evoked increase in intracellular Ca2+ concentration ([Ca2+]i) in cultured rat hippocampal astrocytes using fura-2 or fluo-3 based Ca2+ imaging techniques. ATP at less than 10 nM produced elementary Ca2+ release event "puffs" in a manner independent of extracellular Ca2+. Stimulation with higher ATP concentrations (3 or 10 micro M) resulted in global Ca2+ responses such as intercellular Ca2+ wave. These Ca2+ responses were mainly mediated by metabotropic P2Y receptors. ATP acting on both P2Y1 and P2Y2 receptors produced a transient Ca2+ release by inositol 1,4,5-trisphosphate (InsP3). When cells were stimulated with ATP much longer, the transient [Ca2+]i elevation was followed by sustained Ca2+ entry from the extracellular space. This sustained rise in [Ca2+]i was inhibited by Zn2+ (<10 micro M), an inhibitor of capacitative Ca2+ entry (CCE). CCE induced by cyclopiazonic acid or thapsigargin and Ca2+ entry evoked by ATP share the same pharmacological profile in astrocytes. Taken together, the hierarchical Ca2+ responses to ATP were observed in hippocampal astrocytes, i.e., puffs, global Ca2+ release by InsP3, and CCE in response to depletion of InsP3-sensitive Ca2+ stores. It should be noted that these Ca2+ signals and their modulation by Zn2+ could occur in the hippocampus in situ since both ATP and Zn2+ are rich in the hippocampus and could be released by excitatory stimulation.     

Plasmid-encoded asp operon confers a proton motive metabolic cycle catalyzed by an aspartate-alanine exchange reaction

Tetragenococcus halophila D10 catalyzes the decarboxylation of L-aspartate with nearly stoichiometric release of L-alanine and CO(2). This trait is encoded on a 25-kb plasmid, pD1. We found in this plasmid a putative asp operon consisting of two genes, which we designated aspD and aspT, encoding an L-aspartate-beta-decarboxylase (AspD) and an aspartate-alanine antiporter (AspT), respectively, and determined the nucleotide sequences. The sequence analysis revealed that the genes of the asp operon in pD1 were in the following order: promoter --> aspD --> aspT. The deduced amino acid sequence of AspD showed similarity to the sequences of two known L-aspartate-beta-decarboxylases from Pseudomonas dacunhae and Alcaligenes faecalis. Hydropathy analyses suggested that the aspT gene product encodes a hydrophobic protein with multiple membrane-spanning regions. The operon was subcloned into the Escherichia coli expression vector pTrc99A, and the two genes were cotranscribed in the resulting plasmid, pTrcAsp. Expression of the asp operon in E. coli coincided with appearance of the capacity to catalyze the decarboxylation of aspartate to alanine. Histidine-tagged AspD (AspDHis) was also expressed in E. coli and purified from cell extracts. The purified AspDHis clearly exhibited activity of L-aspartate-beta-decarboxylase. Recombinant AspT was solubilized from E. coli membranes and reconstituted in proteoliposomes. The reconstituted AspT catalyzed self-exchange of aspartate and electrogenic heterologous exchange of aspartate with alanine. Thus, the asp operon confers a proton motive metabolic cycle consisting of the electrogenic aspartate-alanine antiporter and the aspartate decarboxylase, which keeps intracellular levels of alanine, the countersubstrate for aspartate, high.     

Crystal structure of the liganded anti-gibberellin A(4) antibody 4-B8(8)/E9 Fab fragment

Gibberellins, a class of plant hormones, consist of more than 120 members. Only a few of them are recognized by a receptor that remains unknown. The haptenic mouse monoclonal antibody, 4-B8(8)/E9, was generated against gibberellin A(4) (GA(4)) to recognize biologically active GA selectivity, and we attempted to confirm the binding properties between the antibody and GA(4). We carried out an X-ray crystallographic analysis of the 4-B8(8)/E9 Fab fragment complexed with GA(4) at a 2.8 A resolution by using the molecular replacement method. The crystal structure of the Fab fragment showed the typical immunoglobulin fold of the beta-barrel structure which is the common motif of all antibodies. A small hapten-combining site was made up of three heavy chain CDR loops. On the other hand, CDRs of the light chain did not interact directly with GA(4). The C/D rings of the GA(4) molecule were in van der Waals contact mainly with the aromatic side chain of Tyr100AH and Phe100BH of CDR-H3. The 3 beta-hydroxyl and 6 beta-carboxyl groups were, respectively, hydrogen-bonded to the main chain of Ala33H and to the Thr53H heavy chain.