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1.
Gabriela Sánchez-Mejorada Horacio Merchant-Larios Francisco Alonso-deFlorida Luis B. Morales 《Bulletin of mathematical biology》1994,56(1):147-160
Are there enough mast cells in denervated skeletal muscle to account for autopharmacological mediation of the antigen potentials (APs) elicited by microtaps? Through rough qualitative estimations, some authors have suggested a positive answer to this question. However, in view of measurements performed in this investigation of both the density of mast cells and the diffusion coefficient of antigens, the probability of such mediated effects was found to be relatively low:P=0.016 for egg albumin andP=0.004 for ferritin. Therefore, most APs induced by microtaps should be attributed to the direct effect of antigen over the sensitized muscle fibers. Yet, both the density of mast cells found in this work and the known amount of histamine they are capable of releasing when challenged with antigen, support the hypothesis regarding the involvement of these cells when antigen is massively superfused so as to induce Schultz-Dale reactions in muscle strips. Under this circumstance, the direct and mediated mechanisms may coexist. 相似文献
2.
Gloria del Solar Gabriela Kramer Sara Ballester Manuel Espinosa 《Molecular & general genetics : MGG》1993,241(1-2):97-105
Deletion of a region of the promiscuous plasmid pLS1 encompassing the initiation signals for the synthesis of the plasmid lagging strand led to plasmid instability in Streptococcus pneumoniae and Bacillus subtilis. This defect could not be alleviated by increasing the number of copies (measured as double-stranded plasmid DNA) to levels similar to those of the wild-type plasmid pLS1. Our results indicate that in the vicinity of, or associated with the single-stranded origin region of pLS1 there is a plasmid component involved in its stable inheritance. Homology was found between the DNA gyrase binding site within the par region of plasmid pSC101 and the pLS1 specific recombination site RSR. 相似文献
3.
Paulino Bambi Alan M. Tonin Renan de Souza Rezende Fernando Carvalho Vieira Fernanda Gabriela Graciano Miranda Luz Boyero José F. Gonçalves Júnior 《Biotropica》2023,55(1):40-52
Riparian forests play an important role in stream ecosystems, as they support biodiversity, reduce water erosion, and provide litter that fuels aquatic biota. However, they are affected by great array of anthropogenic threats (e.g., fire, logging, and organic pollution), which alter species composition and their physical structure. Although forest recovery after disturbance such as logging can take decades, the legacy of forest clear-cut logging on key processes in tropical riparian ecosystems is mostly unknown. Here, we investigated how litter inputs (leaves, twigs, and reproductive parts) and storage, key processes for carbon and nutrient recycling and for forest and stream biota, are influenced by riparian vegetation undergoing succession (after 28 years from logging) through the comparison of reference and logged forest sites in the Cerrado biome. Litterfall was overall similar between forest types, but litterfall of twigs was twofold higher at logged than reference sites. Similarly, litter inputs from the bank to the stream (i.e., lateral inputs) and streambed storage were 50–60% higher at logged than reference sites. The higher litterfall observed in logged forests could be related to higher proportion of tree species that are characteristic of primary and secondary successional stages, including fast-growing and liana species, which often are more productive and common in anthropogenic areas. Our results showed that the legacy impact of clear-cut logging, even if residual woody vegetation is maintained in riparian buffers, can shift the type, quantity, and seasonality of litter subsidies to tropical streams. This knowledge should be considered within the context of management and conservation of communities and ecosystem processes in the forest-stream interfaces. 相似文献
4.
Phosphorylation and dephosphorylation of ribosomal proteins have been suggested to participate in the regulation of protein synthesis in eukaryotic organisms. The present research focuses on the purification and partial characterization of a protein kinase from maize ribosomes that specifically phosphorylates acidic ribosomal proteins. Ribosomes purified from maize axes were used as the enzyme source. Purification of ribosomes was performed by centrifugation through a 0.5 M sucrose, 0.8 M KCl cushion. A protein kinase activity present in this fraction was released by extraction with 1.5 M KCl and further purified by diethylaminoethyl cellulose column chromatography. A peak containing protein kinase activity was eluted around 400 m M KCl. Analysis of this fraction by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed one band of 38 kDa molecular mass, which cross-reacted in a western blot with antibodies raised against proteins from the large ribosomal subunit. This enzyme specifically phosphorylates one of the acidic ribosomal proteins (P2 ). Its activity is inhibited by Ca2+ and Zn2+ and is activated by Mg2+ , polylysine and spermine. The relevance of this protein kinase in reinitiating the protein synthesis process during germination is discussed. 相似文献
5.
6.
Gabriela Vizárová 《Biologia Plantarum》1975,17(5):380-382
The excretion of cytokinins into the cultivating medium, which are produced by the phytopathogenic fungiMonilia sp. andCytospora sp. has been investigated. All the isolates of the fungi used in the experiments (Monilia fructicola, Monilia fructigena, isolate 2 and 4,Monilia laxa isolate 3 andCytospora sp. isolate CPL and C1) have been found to produce cytokinins. The production is increased during the formation of the fructification organs. Among the isolates investigatedMonilia fructigena isolate 4 andCytospora sp. isolate CPL showed the highest production of cytokinins. After chromatographic separation, cytokinin activity was found at RF 0.7–0.8 values by the biological test as well as by identification according to UV spectra. Application of purified cytokinins produced by the fungi evoked the formation of “green islands” on isolated barley leaves underin vitro conditions. 相似文献
7.
C Ehresmann P Stiegler G A Mackie R A Zimmermann J P Ebel P Fellner 《Nucleic acids research》1975,2(2):265-278
Recent progress in the nucleotide sequence analysis of the 16S ribosomal RNA from E. coli is described. The sequence which has been partially or completely determined so far encompasses 1520 nucleotides, i.e. about 95% of the molecule. Possible features of the secondary structure are suggested on the basis of the nucleotide sequence and data on sequence heterogeneities, repetitions and the location of modified nucleotides are presented. In the accompanying paper, the use of the nucleotide sequence data in studies of the ribosomal protein binding sites is described. 相似文献
8.
Evidence for tertiary structural RNA-RNA interactions within the protein S4 binding site at the 5''-end of 16S ribosomal RNA of Escherichia coli.+. 总被引:11,自引:7,他引:4 下载免费PDF全文
Evidence is presented for tertiary structural interaction(s) (interactions(s) between two regions of an RNA molecule that are widely separated in the RNA sequence) within the 5'-one third of the 16S ribosomal RNA of Escherichia coli that constitutes the binding site of protein S4. The two main interacting RNA regions were separated by about 120 nucleotides (sections Q to M) of the 16S RNA sequence. A second, smaller gap, of 13 nucleotides, occurred within section C". The two main interacting regions contain about 150 nucleotides (sections H" to Q) and 160 nucleotides (sections M to C"). They are folded back on one another and, especially in the presence of protein S4, are strongly protected against ribonuclease digestion. The intermediate region (sections Q to M), however, is relatively accessible to ribonucleases in the S4-RNP. By partial removal of subfragments from the RNA complex it was possible to localise the two main interacting sites within sections H" - H and sections I" - C". Three main criteria for the specificity of the RNA-RNA interactions were invoked and satisfied. The possibility of other tertiary structural RNA-RNA interactions occurring in other regions of the 16S RNA is discussed. Finally, all the structural information on the S4-RNP is summarised and a tentative model is proposed. 相似文献
9.
10.
Kathy Darragh Gabriela Montejo‐Kovacevich Krzysztof M. Kozak Colin R. Morrison Clarisse M. E. Figueiredo Jonathan S. Ready Camilo Salazar Mauricio Linares Kelsey J. R. P. Byers Richard M. Merrill W. Owen McMillan Stefan Schulz Chris D. Jiggins 《Ecology and evolution》2020,10(9):3895-3918
In many animals, mate choice is important for the maintenance of reproductive isolation between species. Traits important for mate choice and behavioral isolation are predicted to be under strong stabilizing selection within species; however, such traits can also exhibit variation at the population level driven by neutral and adaptive evolutionary processes. Here, we describe patterns of divergence among androconial and genital chemical profiles at inter‐ and intraspecific levels in mimetic Heliconius butterflies. Most variation in chemical bouquets was found between species, but there were also quantitative differences at the population level. We found a strong correlation between interspecific chemical and genetic divergence, but this correlation varied in intraspecific comparisons. We identified “indicator” compounds characteristic of particular species that included compounds already known to elicit a behavioral response, suggesting an approach for identification of candidate compounds for future behavioral studies in novel systems. Overall, the strong signal of species identity suggests a role for these compounds in species recognition, but with additional potentially neutral variation at the population level. 相似文献