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81.
A new species of Mallomonas, M. nuussuaqensis was found to be common in samples collected from waterbodies on Nuussuaq/Nûgssuaq (70N-71N, West Greenland). The species has very compact silica scales with a thick broad marginal rim and a very thick and broad hood, which often occupies more than two thirds of the shield. 相似文献
82.
Folate responsiveness during growth and development of Dictyostelium: separate but related pathways control chemotaxis and gene regulation 总被引:2,自引:0,他引:2
Folate-controtled gene expression and chemotaxis have been examined in Dictyostelium wild-type and mutant strains. We show that regulation of the discoidin genes is sensitive to foiate in growing ceiis as weli as in suspension development. The signal is transferred via the N10-methylfoiate-sensitive folate receptor sites, which also appear to confer the chemotactic response. The strain HG5145 has previously been isolated as a mutant that does not display chemotactic movement towards folate. Nevertheless, these cells are fully functional in foiate-mediated downregulation of discoidin I expression. The strain ga 93 has been isolated as an overproducer mutant of the cyclic nucleotide phosphodiesterase inhibitor. Simultaneously, these cells fail to downregulate discoidin I in response to folate but are fully functional in folate chemotaxis. Therefore we conclude that the pathways for chemotaxis and for gene regulation diverge downstream of a common receptor type. 相似文献
83.
The nusG gene of Streptomyces griseus: Cloning of the gene and analysis of the A-factor binding properties of the gene product 总被引:1,自引:0,他引:1
Abstract The nusG gene of Streptomyces griseus was cloned and the nucleotide sequence determined. It encodes a protein with an identify of 76% to the reported receptor (VbrA) for VB-C, an autoregulatory factor in Streptomyces virginae . NusG protein was expressed in Escherichia coli . However, no binding activity for A-factor, an butyrolactone autoregulator in S. griseus very similar to VB-C, could be detected. The nusG gene of S. griseus does not seem to encode the A-factor-binding protein. 相似文献
84.
Of the two components of sexual selection, female choice is much less obvious than male-male competition, and hence has always been considered to be of secondary importance. However, recent field observations and new theory have brought about a radical change of emphasis. It now appears that although a female's choice of who fathers her offspring often occurs in a subtle manner, it may be widespread and take place through a variety of behavioural and physiological mechanisms, including the manipulation of male behaviour and the selection of sperm within the female reproductive tract. 相似文献
85.
Sieghart Sopper Susanne Hemm Jürgen Meixensberger Cheik Coulibaly Christiane Stahl-Hennig Gerhard Hunsmann Bernhard Fleckenstein Volker ter Meulen Rüdiger Drries 《Journal of medical primatology》1993,22(2-3):138-146
Paired sera and CSF samples were collected from SIVmac-infected macaques. Animals infected with SIVmac251 maintained low gag and high env-specific antibody levels in plasma. Increasing env-specific antibody titers in CSF were associated in one animal with strong intrathecal synthesis. SIVmac239-infected monkeys revealed high antibody titers of gag and env-specificity, in one animal accompanied by weak intrathecal synthesis of virus-specific antibodies. In all animals, the CD4/CD8 ratio in CSF decreased faster compared to blood. 相似文献
86.
Stupperich E Eisinger HJ Kerssebaum R Nexø E 《Applied and environmental microbiology》1993,59(2):599-603
The homoacetogenic bacterium Sporomusa ovata synthesized the vitamin B(12) analog phenolyl cobamide or 4-fluorophenolyl cobamide when the methanol medium of growing cells was supplemented with 10 mM phenol or 5 mM 4-fluorophenol. Phenol and, presumably, 4-fluorophenol were specifically incorporated into these cobamides, since phenol was not metabolized significantly into amino acids or into acetic acid, the product of the catabolism. The phenol-containing cobamides contributed up to 90% of the protein-bound cobamides of the 1,300 to 1,900 nmol of corrinoid per g of dry cell material formed. Fluorine-19 nuclear magnetic resonance spectroscopy of 4-fluorophenolyl cobamide exhibited a resonance near 30 ppm. An additional signal emerged at 25 ppm when 4-fluorophenolyl cobamide was investigated as the cofactor of a corrinoid-dependent protein. The two resonances indicated distinct cofactor arrangements within the protein's active site. A 5-ppm high-field shift change suggested van der Waal's interactions between the fluorinated nucleotide of the cofactor and adjacent amino acid residues of the enzyme. Similarly, Propionibacterium freudenreichii and Methanobacterium thermoautotrophicum synthesized 5-fluorobenzimidazolyl cobamide. The human corrinoid binders intrinsic factor, transcobalamin, and haptocorrin recognized this corrinoid like vitamin B(12). Hence, it is possible to use F-labeled nuclear magnetic resonance spectroscopy for analyses of protein-bound cobamides. 相似文献
87.
T. Mastrocola I. H. Lambert B. Kramhøft M. Rugolo E. K. Hoffmann 《The Journal of membrane biology》1993,136(1):55-62
Trypsinized human skin fibroblasts in suspension perform regulatory volume decrease (RVD) after cell swelling in hypotonic medium. During RVD, 36Cl– efflux is dramatically increased and the cell membrane is depolarized, indicating the activation of Cl– channels. This activation of Cl– channels depends on extracellular as well as on intracellular Ca2+. The swelling-induced Cl– efflux and the RVD response are inhibited by the 5-lipoxygenase inhibitor ETH 615-139. Finally, following hypotonic treatment, cellular pH decreases. The pH decrease does not involve the Cl–/HCO
3
–
exchange because it is independent of the external Cl– concentration.T. Mastrocola was recipient of a scientific fellowship from the Italian Consiglio Nazionale delle Ricerche (C.N.R.). This work was supported by Progetto Finalizzato Ingegneria Genetica, C.N.R., Roma, and by the Danish Natural Research Council. 相似文献
88.
The effective molecular weight cut-off values of dialysis membranes for carrageenan and alginate oligosaccharides were evaluated by gel permeation chromatography and nuclear magnetic resonance spectroscopy. For the different membranes tested, i.e. Medicell, Spectra Por 1000D and 3500D, the porous sizes are analogous to tri- and tetrasaccharides. A simple dialysis can be used to recover the majority of the oligosaccharides produced by a carrageenase or an alginate lyase digestion. 相似文献
89.
The mechanisms of intercommunication between the immune and nervous systems are not fully understood. In the case of the intestine, the enteric nervous system is involved in the regulation of immune responses. It was therefore decided to employ immunohistochemical techniques to investigate the structural organization of the enteric nervous system in Peyer's patches of the porcine small intestine. Using antibodies against various nervous system-specific markers (protein gene product 9.5, neuron-specific enolase, neurofilament 200, S-100 protein and the glial fibrillary acidic protein), an intimate and specific structural association could be demonstrated between enteric nerves and the compartments of Peyer's patches: follicles, interfollicular regions and domes. Peyer's patches have a close topographical relationship to the two submucosal plexuses. Enteric nerves are located around the follicle in the interfollicular area — the so-called traffic area-and in the dome area, which plays an important role in the uptake and presentation of antigens. 相似文献
90.
Summary Reproductive value (RV) and net reproductive output (R
o) are frequently used fitness measures. We argue that they are only appropriate when intervals between reproductive events are fixed, as they are dimensionless generation-to-generation scalings with units offspring per parent. A fitness measure should account for two different effects of a decrease in generation time: (1) increased survival due to shorter exposure to mortality agents and (2) increased frequency of reproduction.R
o andRV deal with the first of these two effects, while a measure with a physical dimensionper time [T–1] is needed to account for the second. The Malthusian growth parameter,r, meets this requirement and in situations where time to reproduction is variable, we propose, the instantaneous rate of spread of descendants (from an individual) be used instead ofR
o. As an alternative toRV, we suggest using the instantaneous difference = –r, wherer is the population rate of increase. WhileRV andR
o are dimensionless ratios, , and areper time rates which are appropriate in accounting for alterations in generation time. 相似文献