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41.
C Ramos I Sch?dtler-Siwon L Ortiz-Ortiz 《Journal of immunology (Baltimore, Md. : 1950)》1979,122(4):1243-1247
Infection with Trypanosoma cruzi decreases the ability of spleen cells from mice to respond to either T cell, concanavalin A (Con A), or B cell, lipopolysaccharide (LPS), mitogens. The effect of infection on the mitogenic response depends on the elapsed time between the day of infection and the time of mitogen presentation. Responses early in infection are normal, whereas later responses to either mitogen are depressed. Spleen cells from late trypanosome-infected mice inhibit the ability of normal spleen cells to respond to Con A or LPS. The cell in the T. cruzi-infected spleen cells responsible for this effect is nonadherent, sensitive to treatment with anti-mouse thymus serum plus complement, but insensitive to treatment with anti-immunoglobulin plus complement. These data indicate that infection with T. cruzi elicits over time the generation of T cells suppressive to T and B cell mitogenic responses. 相似文献
42.
In 60 objects the participation of splenic vessels in human pancreas blood supply was studied roentgeno-angiographically and by means of anatomical preparation. Morphometrical data obtained were treated by computers "Minsk-22" and "M-220-M" to calculate main statistic values and their correlations. Some recommendations of applied importance for pancreas surgery were suggested. Maximal and minimal dimensions of the pancreas segments, which can be used for grafting with the following blood supply restoration in the transplant at the expense of the splenic vessels only, were represented. 相似文献
43.
Carmen Michán Birgit Kessler Victor de Lorenzo Kenneth N. Timmis Juan L. Ramos 《Molecular & general genetics : MGG》1992,235(2-3):406-412
Summary The XylS protein is the positive regulator of the TOL plasmid-encoded meta-cleavage pathway for the metabolism of alkylbenzoates in Pseudomonas putida. This protein is activated by a variety of benzoate analogues. To elucidate the functional domains of the regulator and their interactions, several fusions of the XylS C-terminus to MS2 polymerase and of the N-terminus to -galactosidase were constructed but all are inactive. In addition, 15 double mutant xylS genes were constructed in vitro by fusing parts of various mutant genes to produce mutant regulators exhibiting C-terminal and N-terminal amino acid substitutions. The phenotypic properties of the parental single mutant genes, and those of the double mutant genes, suggest that the C-terminal region is involved in binding to DNA sequences at the promoter of the meta-cleavage pathway operon, and that the benzoate effector binding pocket includes critical residues present at both the N-terminal and C-terminal ends of the protein. The intraallelic dominance of the Ile229 (Ser229 Ile) and Val274 (Asp274 Val) substitutions over the N-terminal His4l (Arg4l His) substitution, and the intraallelic dominance of Thr45 (Arg45 Thr) over Ile229 and Val274, support the proposal that these two regions of the regulator interact functionally. Combination of the Leu88 (Trp88 Leu) and Arg256 (Pro256 Arg) substitutions did not suppress the semiconstitutive phenotype conferred by Leu88, but resulted in a protein with altered ability to recognize benzoates. In contrast, the Leu88 semiconstitutive phenotype was suppressed by Va1288 (Asp288 Val), and the double mutant was susceptible to activation by benzoates. The results suggest that intramolecular interactions between the C- and N-terminal regions of XylS are critical for activation of the regulator by the effector. 相似文献
44.
Conjugational transfer of recombinant DNA in cultures and in soils: host range of Pseudomonas putida TOL plasmids. 总被引:7,自引:3,他引:4
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Recombinant TOL plasmid pWWO-EB62 allows Pseudomonas putida to grow on p-ethylbenzoate. This plasmid can be transferred to other microorganisms, and its catabolic functions for the metabolism of alkylbenzoates are expressed in a limited number of gram-negative bacteria, including members of pseudomonad rRNA group I and Escherichia coli. Transfer of the recombinant plasmid to Erwinia chrysanthemi was observed, but transconjugants failed to grow on alkylbenzoates because they lost catabolic functions. Pseudomonads belonging to rRNA groups II, III, and IV, Acinetobacter calcoaceticus, and Alcaligenes sp. could not act as recipients for TOL, either because the plasmid was not transferred or because it was not stably maintained. The frequency of transfer of pWWO-EB62 from P. putida as a donor to pseudomonads belonging to rRNA group I was on the order of 1 to 10(-2) transconjugant per recipient, while the frequency of intergeneric transfer ranged from 10(-3) to 10(-7) transconjugant per recipient. The profile of potential hosts was conserved when the donor bacterium was Escherichia coli or Erwinia chrysanthemi instead of P. putida. No intergeneric gene transfer of the recombinant TOL plasmid was observed in soils; however, intraspecies transfer did take place. Intraspecies transfer of TOL in soils was affected by the type of soil used, the initial inoculum size, and the presence of chemicals that could affect the survival of the donor or recipient bacteria. 相似文献
45.
To assess the possibility that vasoactive intestinal polypeptide (VIP) plays a role in naturally occurring changes in prolactin secretion in ring doves, we used immunohistochemical techniques to measure VIP-like immunoreactivity in the brain as a function of stage of the reproductive cycle. Differences between parental and nonparental birds in VIP profiles were detected in the ventral portion of the infundibular region. More specifically, there is an increase in cell size and staining intensity in the ventral infundibulum of breeding birds compared to simultaneously processed tissue taken from control animals. In both sexes, an increase in size of VIP-like immunoreactive cells is detectable during courtship and early incubation, anticipating the increase in plasma prolactin levels. VIP cell size remains elevated from about Incubation Day 14 to Brooding Day 14, and a steady decrease is observed during the remaining posthatching period, as squab begin to feed independently. Compared to parents rearing one squab, those with two young have a prolonged interval of increased infundibular VIP immunoreactivity. Furthermore, doves with no previous experience of a breeding cycle exhibit prolonged VIP-like immunoreactivity compared to experienced parents, paralleling previously described differences between these groups in parental behavior. 相似文献
46.
Allen M. Schoffstall Robert J. Barto David L. Ramos 《Origins of life and evolution of the biosphere》1982,12(2):143-151
Nucleosides or deoxynucleosides were converted to a number of phosphorylated nucleotide and deoxynucleotide derivatives by ammonium or alkali dihydrogen phosphates in formamide. Conversions were smaller and slower at room temperature and greater and faster at elevated temperatures. Nucleotides afforded product mixtures similar to those obtained for nucleosides under the same conditions, indicating the occurrence of transphosphorylation processes. Products of reaction at elevated temperatures were cyclic nucleotides, nucleoside monophosphates, nucleoside diphosphates and cyclic nucleotide phosphates. The relative amounts of products formed were quite temperature dependent. Cyclic nucleotides were found to be in greatest abudance for reactions run at 125° or above. Relative yields of 2, 3 and 5 nucleotides and 3 and 5 deoxynucleotides from several experiments are reported. 5-Monophosphates were generally found to be present in larger quantities than 2 or 3 monophosphates. 2-Deoxyadenosine showed a preference for phosphorylation at the 3 position. Conclusions reached from mechanistic studies are that the phosphorylations are a series of equilibrium reactions, with cyclic nucleotides being formed irreversibly.Presented in part at the 3rd Northwest and 5th Rocky Mountain Joint Regional ACS Meeting of the American Chemical Society, Salt Lake City, Utah, June, 1980. 相似文献
47.
Two asparagine synthetases in Saccharomyces cerevisiae 总被引:3,自引:0,他引:3
In Saccharomyces cerevisiae L-asparagine auxotrophy, resulting from a lack of L-asparagine synthesis, needs simultaneous defects in two genes. This unusual situation is shown to result from the occurrence of two L-asparagine synthetases. The meaning of this duplication remains obscure. The properties of the two enzymes are remarkably similar: both have a molecular weight of 150,000 and they exhibit a slight repression and a similar inhibition by asparagine. Neither one is located in mitochondria and both are probably cytosolic. Their identification so far lies only in their behaviour on ion-exchange chromatography and in the encoding genes. 相似文献
48.
During the process of degradation of the cell wall of the yeast form of Pullularia pullulans by the lytic system of Micromonospora chalcea samples were withdrawn at different times and observed under phase contrast and electron microscope. The progressive lysis of the walls reveals a fibrillar component inside the apparently amorphous wall. Freeze etched preparations of cells during the formation and regeneration of protoplasts show that the cellular membrane is split and this method allows the smooth external face of the membrane and other internal face covered by particles to be seen. The fact that the smooth face of the membrane is only visible during the preparation or the regeneration of protoplasts and very rarely when intact cells are fractured, suggests a strong adherence between cell wall and this external layer of the membrane. During the regeneration which takes place as in most of the yeasts and moulds, a special study of the extension of the cell wall is made and a possible mechanism for this extension of the regenerated cell wall is proposed. 相似文献
49.
Ping Li Niloofar Nayeri Kamil Grecki Eva Ramos Becares Kaituo Wang Dhani Ram Mahato Magnus Andersson Sameera S. Abeyrathna Karin LindkvistPetersson Gabriele Meloni Julie Winkel Missel Pontus Gourdon 《Protein science : a publication of the Protein Society》2022,31(7)
Copper (Cu) is one of the most abundant trace metals in all organisms, involved in a plethora of cellular processes. Yet elevated concentrations of the element are harmful, and interestingly prokaryotes are more sensitive for environmental Cu stress than humans. Various transport systems are present to maintain intracellular Cu homeostasis, including the prokaryotic plasmid‐encoded multiprotein pco operon, which is generally assigned as a defense mechanism against elevated Cu concentrations. Here we structurally and functionally characterize the outer membrane component of the Pco system, PcoB, recovering a 2.0 Å structure, revealing a classical β‐barrel architecture. Unexpectedly, we identify a large opening on the extracellular side, linked to a considerably electronegative funnel that becomes narrower towards the periplasm, defining an ion‐conducting pathway as also supported by metal binding quantification via inductively coupled plasma mass spectrometry and molecular dynamics (MD) simulations. However, the structure is partially obstructed towards the periplasmic side, and yet flux is permitted in the presence of a Cu gradient as shown by functional characterization in vitro. Complementary in vivo experiments demonstrate that isolated PcoB confers increased sensitivity towards Cu. Aggregated, our findings indicate that PcoB serves to permit Cu import. Thus, it is possible the Pco system physiologically accumulates Cu in the periplasm as a part of an unorthodox defense mechanism against metal stress. These results point to a previously unrecognized principle of maintaining Cu homeostasis and may as such also assist in the understanding and in efforts towards combatting bacterial infections of Pco‐harboring pathogens. 相似文献
50.
Masuda HP Ramos GB de Almeida-Engler J Cabral LM Coqueiro VM Macrini CM Ferreira PC Hemerly AS 《FEBS letters》2004,574(1-3):192-202
Eukaryotic DNA replication requires an ordered and regulated machinery to control G1/S transition. The formation of the pre-replicative complex (pre-RC) is a key step involved in licensing DNA for replication. Here, we identify all putative components of the full pre-RC in the genome of the model plant Arabidopsis thaliana. Different from the other eukaryotes, Arabidopsis houses in its genome two putative homologs of ORC1, CDC6 and CDT1. Two mRNA variants of AtORC4 subunit, with different temporal expression patterns, were also identified. Two-hybrid binary interaction assays suggest a primary architectural organization of the Arabidopsis ORC, in which AtORC3 plays a central role in maintaining the complex associations. Expression profiles differ among pre-RC components suggesting the existence of various forms of the complex, possibly playing different roles during development. In addition, the expression of the putative pre-RC genes in non-proliferating plant tissues suggests that they might have roles in processes other than DNA replication licensing. 相似文献