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31.
He-T sequences are a complex repetitive family of DNA sequences in Drosophila that are associated with telomeric regions, pericentromeric heterochromatin, and the Y chromosome. A component of the He-T family containing open reading frames (ORFs) is described. These ORF-containing elements within the He-T family are designated T-elements, since hybridization in situ with the polytene salivary gland chromosomes results in detectable signal exclusively at the chromosome tips. One T-element that has been sequenced includes ORFs of 1,428 and 1,614 bp. The ORFs are overlapping but one nucleotide out of frame with respect to each other. The longer ORF contains cysteine-histidine motifs strongly resembling nucleic acid binding domains of gag-like proteins, and the overall organization of the T-element ORFs is reminiscent of LINE elements. The T-elements are transcribed and appear to be conserved in Drosophila species related to D. melanogaster. The results suggest that T-elements may play a role in the structure and/or function of telomeres.by W. Hennig  相似文献   
32.
The effect of ozone exposure on the activities of reactive oxygen scavenging enzymes (SOD†, catalase, GSH-Px) in RBC of Japanese charr (Salvelinus leucomaenis) was examined. Ozone (0, 0.4 and 0.7 ppm as initial concentrations) was exposed to Japanese charr for 30 min, which definitely caused serious membrane damage to RBC of fish. Ozone exposure at 0.4 and 0.7 ppm decreased activities of both catalase and GSH-Px by 80 to 57+ of the control. On the other hand, the activities of SOD remained unaffected even by 0.7 ppm ozone exposure. A hypothesis on the RBC membrane damage and participation of SOD and heme-iron was proposed.  相似文献   
33.
The internal cation levels of chloroplasts isolated from a green sea alga, Bryopsis maxima, were studied. Atomic absorption spectroscopy, combined with the determination of the sorbitol-impermeable and water-permeable spaces, revealed that chloroplasts contain an extremely high concentration of K+ and high levels of Na+, Mg2+ and Ca2+. A method was developed to estimate the thermodynamic activities of monovalent and divalent cations present in chloroplasts. pH changes induced by the addition of an ionophore (plus an H+ carrier), which makes the outer limiting membranes of chloroplasts permeable to both a cation and H+, were determined. Provided that the external pH was set equal to the internal pH, the internal concentration of the cation was estimated by determining the external cation concentration which gave rise to no electrochemical potential difference of the cation and hence no pH change on addition of the ionophore. The internal pH was determined by measuring distributions of radioactive methylamine and 5,5-dimethyloxazolidine-2,4-dione between the chloroplast and medium (Heldt, H.W., Werdan, K., Milovancev, M. and Geller, G. (1973) Biochim. Biophys. Acta 314, 224–241). The internal pH was also estimated by measuring pH changes caused by the disruption of the outer limiting membrane with Triton X-100. The results indicate that a significant part of the monovalent cations and most of the divalent cations are attracted into a diffuse layer adjacent to the negatively charged surfaces of membranes and proteins, or form complexes with organic and inorganic compounds present in the intact chloroplasts.  相似文献   
34.
The distribution of nitrate and nitrite in the interstitial water of the sediment of eelgrass (Zostera marina) bed of Izembek Lagoon, Alaska, were investigated. Their concentrations were relatively high (0 to 9.8 μg-at.N·1?1, average 4.8 for nitrate; 0 to 4.0 μ-at.N·1?1, average 1.9 for nitrite) although the sediments were anoxic and contained hydrogen sulphide. The rates of bacterial denitrification measured by 15N tracer technique ranged from 0.49×10?10 to 1.2 × 10?9 g-atN·g?1·h?1. When a steady state is maintained, the loss of nitrate and nitrite must be balanced by their production by bacterial nitrification. Experimentally determined rate of nitrification in the sediment was of the same order. A model experiment demonstrated that oxygen is transported from leaves to rhizomes and roots of eelgrass and released into the sediment. The oxygen is used for nitrification in the rhizosphere in anoxic sediments.  相似文献   
35.
Denitrification and Ammonia Formation in Anaerobic Coastal Sediments   总被引:23,自引:18,他引:5       下载免费PDF全文
Simultaneous determinations of nitrogen gas production, ammonia, and particulate organic nitrogen formation in the coastal sediments of Mangoku-Ura, Simoda Bay, and Tokyo Bay were made by using the 15N-label tracer method. The rate of nitrogen gas production in the sediment surface layer was about 10−2 μg atom of N per g per h, irrespective of the location of the sediments examined. [15N]ammonia and -particulate organic nitrogen accounted for 20 to 70% of the three products, and after several hours of incubation, the major fraction of nondenitrified 15N in Mangoku-Ura and Simoda Bay sediments was recovered as ammonia. In Tokyo Bay sediments, particulate organic nitrogen was produced at a greater rate than was ammonia. The reduction rate data suggest that the pathway of nitrate reduction to ammonia is important in coastal sediments.  相似文献   
36.
The cell surface engineering system, in which functional proteins are genetically displayed on microbial cell surfaces, has recently become a powerful tool for applied biotechnology. Here, we report on the surfactant modification of surface-displayed lipase to improve its performance for enzymatic synthesis reactions. The lipase activities of the surfactant-modified yeast displaying Rhizopus oryzae lipase (ROL) were evaluated in both aqueous and nonaqueous systems. Despite the similar lipase activities of control and surfactant-modified cells in aqueous media, the treatment with nonionic surfactants increased the specific lipase activity of the ROL-displaying yeast in n-hexane. In particular, the Tween 20-modified cells increased the cell surface hydrophobicity significantly among a series of Tween surfactants tested, resulting in 8–30 times higher specific activity in organic solvents with relatively high log P values. The developed cells were successfully used for the enzymatic synthesis of phospholipids and fatty acid methyl esters in n-hexane, whereas the nontreated cells produced a significantly low yield. Our results thus indicate that surfactant modification of the cell surface can enhance the potential of the surface-displayed lipase for bioconversion.  相似文献   
37.
Summary Production of phospholipase D (PLD) by Streptoverticillium cinnamoneum immobilized within porous particles was investigated in repeated batch fermentation. The enzyme productivity in repeated batch fermentation was 2.2-fold that obtained in batch fermentation without immobilization, since many of the immobilized cells could be utilized as seed cells for each subsequent batch cycle.  相似文献   
38.
We investigated the expression of KIT (product of c-kit oncogene), gain-of-function mutations, and activation of its downstream signal transduction in human testicular cancers. KIT was expressed in 88% (22/25) of seminomas and in 44.4% (4/9) of non-seminomas compared to adjacent normal testicular tissue. Nine of the KIT-expressing seminomas had mutations (40.9%; 9/22) in the c-kit gene; two cases in exon 11 and 7 cases in exon 17. Two of these mutations in exon 17 were novel, and the other seven mutations were identical to the already known gain-of-function mutations which cause activation of KIT without ligand stem cell factor. All of the mutant KIT and 53.8% (7/13) of wild-type KIT were phosphorylated (activated) and associated with phosphorylated phosphatidylinositol 3-kinase (PI3K). Akt was also phosphorylated in these seminomas, suggesting that the KIT-PI3K-Akt pathway is activated in seminoma. These findings suggest that the KIT-PI3K-Akt pathway is constitutively activated in testicular germ cell tumors, due to overexpression of KIT protein and/or gain-of-function mutations in the c-kit gene.  相似文献   
39.
A cDNA clone encoding a novel papain-like cysteine protease was isolated from wheat germ (Triticum aestivum). This cDNA encoded a 371-residue protein, designated WCP2, composed of signal peptide followed by a propeptide and a mature protease containing active site residues that are highly conserved among the papain family. The mature WCP2 protein (26 kDa) was detected in the quiescent embryo and its level of expression in the germinating embryo was greatly increased.  相似文献   
40.
DOCK proteins constitute a family of evolutionarily conserved guanine nucleotide exchange factors (GEFs) for Rho family of GTPases. Although DOCK family proteins do not contain the Dbl homology domain typically found in GEFs, they mediate the GTP–GDP exchange reaction through DHR-2 domain. Accumulating evidence indicates that the DOCK proteins act as major GEFs in varied biological settings. For example, DOCK2, which is predominantly expressed in hematopoietic cells, regulates migration and activation of leukocytes through Rac activation. On the other hand, it was recently reported that mutations of DOCK8, another member of the DOCK family proteins, cause a combined immunodeficiency syndrome in humans. This article reviews the structure, functions and signaling of DOCK2 and DOCK8, especially focusing on their roles in immune responses.  相似文献   
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