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This paper is an attempt to describe and analyze in formal terms a genetic circuit which is rather complex and reasonably well disentangled: the control of immunity in lambdoid bacteriophages. Known models are expressed as logic equations, which relate the stade of activity of genes to variables of three kinds: genetic variables which describe the genotype of the organism, environmental variables like temperature and memorization variables. The value of each memorization variable (presence or absence of a gene product) is related to the value of the corresponding function (operation or not of the gene) by two characteristic time delays, an «establishment delay and a «decay delay.From the equations, one can derive matrices which facilitate comparison between models by showing which stable states are predicted by each model. Implications of current models, which had apparently remained cryptic, have been realized and experimentally tested.From the matrices, one can derive graphs which show the pathways (sequences of states) consistent with each model. These graphs are frequently branched and in these cases one has to analyze which conditions determine that one pathway rather than another one, is followed. 相似文献
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In the context of the collective research program “functional technology of solutrean points”, conducted from 1987 to 2000, more than 300 impacts were experimentally produced on ungulate carcasses (goat, cow, horse). Based on the classification of these types of impacts proposed by P. Morel in 1991, we can estimate that only the inclusions of point fragments in the bones remain diagnostic in most archaeological contexts. The other types, such as scrapings or splittings, can be confused with tool traces, carnivore tooth marks or postdepositional alterations. P. Morel has published the results for small herbivores, and we present our results here for large herbivores. More than 200 stigmata were observed on the carcasses of an adult cow and horse following experimental shots with solutrean projectiles (shouldered points, laurel leaf points and willow leaf points) and a few reindeer antler points. These traces are concentrated around the vital parts of the animals. The most common types are marginal scrapings and splittings, but implantations are more numerous than on small ungulate skeletons. This numerically significant body of data is derived from carefully controlled experiments. Indispensable for the interpretation of the stigmata observed on bones found in Paleolithic sites, such experiments contribute to our knowledge of the conditions prey exploitation and allow us to address questions concerning the fossilization of these traces and their apparent frequency. 相似文献
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Preliminary Study of the Effects of Impoundment of LG-2 Reservoir (James Bay Territory, Quebec) on the Net Seston and the Zooplankton of Impounded Rivers and Lakes The effects of impoundment on the biomass of net seston and zooplankton in lakes and rivers of Northern Quebec were investigated from 1978 to 1980, before, during and after the completion of LG2 Reservoir on the River La Grande (53° 54′ N, 76° 78′ W). In lotic stations, a 41–77% decrease in net seston was observed due to sedimentation of mineral particles (36–80 mg/m3 in 1978 to 10–21 mg/m3 in 1979). The ratio of organic to total seston increased from an average of 0.18 before the impoundment to 0.65 after. The flooding phase brought about a trophic upsurge; the biomass of the zooplankton increased by one to two orders of magnitude at the various sites; the greatest increases occurred in the central stations near the dam, the smallest in the upper stations near the inflow. In lake stations, no significant difference between years could be detected; the mean zooplankton biomass for all three years ranged from 6.59 mg/m3 to 34.34 mg/m3. Spatial variations between lakes were however significant. Results are compared with those in other natural lakes in Canada and reservoirs in the United States. Comparative examination of phytoplankton biomass before and after impoundment of LG2 Reservoir suggests that bacterioplankton and allochthonous organic material are key elements in the pelagic food chain after impoundment. 相似文献
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Résumé Des élevages expérimentaux deCallosobruchus maculatus (F.) (Coleoptera, Bruchidae) sur les graines deVicia faba décortiquées ou non, ou sur des pastilles faites des mêmes graines, ont permis de mettre en évidence une barrière empêchant le développement de la bruche.Avec les graines entières, toutes les larves meurent au premier stade enfoncées dans le tégument; alors qu'elles se développent normalement dans les graines décortiquées.Avec des pastilles de broyats de graines non décortiquées, la majorité des larves meurt avant le terme de leur développement; la plus forte mortalité est observée au quatrième stade larvaire. Les larves, qui survivent, accusent une augmentation de leur durée de développement par rapport à celles qui se nourrissent aux dépens des pastilles faites de graines sans tégument. 相似文献
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Elisabeth Alliot Annie Pastoureaud Joël Trellu 《Biochemical Systematics and Ecology》1980,8(4):441-445
The activities of digestive enzymes were studied during the course of larval development (from hatching to 30 days) in the sole, Solea solea. No glycosidase activity was present, but alkaline proteolytic activity increased from hatching to day 5, then decreased until day 15. In the acid range, proteolytic activity was relatively stable from the 10th to the 30th day. There were also changes in the number of esterase-like isozymes which increased between day 20 and 30, with minimum activity observed during metamorphosis. 相似文献
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M. Daune 《Biopolymers》1969,7(5):659-670
The theory of polyelectrolyte solution of Alexandrowicz: and Katchalsky is used to calculate the electrostatic potential of single stranded polynucleotides for different ionic strength. We have considered the potential of double stranded DNA as the superposition of the different potentials produced by each chain, provided the average distance between the strands is higher than an ionic strength-dependent parameter b. For ionic strength lower than 5 × 10?2M, the assumption is no longer valid, and a cylindrical model with a uniform charge density must be used. The continuity between the two models was tested, and thus we can calculate the electrical potential at the vicinity of a phosphate group in the whole range of ionic-strength where the double helix is stable. It was therefore possible to determine the theoretical number of ions bound electrostatically to DNA and we found an increase of ion binding with a decrease of ionic strength. Such a model was further applied to the change of specific volume in different salt solutions. Comparison is made with recent pycnometric data on Na? and Cs? salts of DNA. Agreement is good in the case of Cs+, but for Na+, cation binding is likely to be accompanied by a change of the hydration of DNA, which depends on ionic strength. With the same model we can see easily the ion-trapping properties of DNA which play an important role in any formation of complex between heavy ions and bases. 相似文献
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The binding of cupric ion (Cu++) to DNA was followed by spectrophotometry, melting profiles, and hydrodynamic techniques, in 0. 1M NaClO4 and at pH 5. 6. A small amount of Cu++ is bound specifically to bases (about 1 Cu++ per 20 nucleotides), in agreement with polarographic and EPR data. A preferential stabilization of G–C pairs and only a slight increase of the flexibility of the molecule were observed. In 5 × 10?3M NaClO4, a higher number of nonhomogeneous binding sites is found by spectrophotometry. It is concluded that at least two types of sites are available for Cu++. The first one, where Cu++ is chelating N7 of purines to phosphate, is observed only at low ionic strength and destabilizes the double helix. The second exists mainly at 0, 1M or higher ionic strength. All the sites are identical and could be attributed to two successive guanine residues in the same strand. Similar behavior was found for other divalent cations, e. g., Fe++, Mn++, and Co++. 相似文献
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Isolated abdomens of crayfish were maintained in vitro and lysine (-3H) was intracellularly injected into one of the giant motoneuron of the ventral cord ganglia by iontophoresis. Membrane potentials ranging between -60 and -70 mV were recorded all along the experiment. Light microscope radioautographs showed an intense reaction over the injected nerve cell body and the initial segment of its axon; most of the surrounding tissues were free of radioactivity when the diffusion of the injected lysine (-3H) was prevented by adding cold lysine to the bathing medium. Some exchange of label was however noted with electrically coupled axons and glial sheaths. No radioactive protein could be traced in the numerous nerve endings of the neuromuscular junction. Nonetheless when a ligature was placed on the nerve root, the amount of accumulated radioactivity was increased from 3 to 6 h. in the axon of the injected motoneuron only. Electron microscope radioautographs indicate that the fast transported proteins were mainly associated with the endoplasmic reticulum and the axonal membrane. It is concluded that the visualization of the nerve endings was limited by the dispersion of the label into the numerous thin terminal branchs of the axon; however the combination of iontophoretic injection and radioautography permits to trace endogenous protein along the axon and to study molecular exchanges with other cells. 相似文献
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Des tanins condensés sont extraits et isolés à partir du tégument de Vicia faba var. Géante Portugaise. Quatre polymères sont quantifiés et identifiés à quatre fractions: A, B, C et D. Ces fractions sont incorporées, en mélange ou séparées à différentes concentrations, dans un milieu nutritif favorable au développement de Callosobruchus maculatus (F.) (Coleoptera, Bruchidae).Les composés phénoliques provoquent la mortalité d'une partie de la population et retardent le développement des survivants. La mortalité observée varie suivant les fractions, leurs doses et le stade de développement de la bruche.La barrière constituée par le tégument des fèves est bien de nature chimique et concerne les tanins condensés.Dans un système de production agricole, l'utilisation des cultivars de fèves riches en tanins faiblement condensés pourrait permettre de réduire les taux d'infestation des graines de V. faba par C. maculatus. 相似文献
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Rene Toury 《生物化学与生物物理学报:生物膜》1973,307(3)
Two classes of low-affinity Ca2+-binding sites have been shown to exist. One type dissociates as pH rises, thereby increasing the amount of bound Ca2+. The other type, which does not change in number, has an affinity for Ca2+ which is dependent on ionic strength. The former is possibly a phospholipid, the latter possibly a protein.Under our experimental conditions, the inner mitochondrial membrane contained binding sites of the second class ony while other membranes contain both types. Rough endoplasmic reticulum contains yet another class of sites at the ribosomal level.
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L'existence de deux catégories de sites de fixation de faible affinité du Ca2+ a été mise en évidence. Les uns se dissocient de plus en plus quant le pH s'éléve permettant une augmentation des quantités de Ca2+ fixé, les autres sont invariables en nombre, mais leur affinité pour le Ca2+ est dépendante de la force ionique du milieu. Les premiers pourraient étre de nature phospholipidique, les seconds de nature protéique.Dans nos conditions expérimentales, la membrane interne des mitochondries possède uniquement des sites de la seconde catégorie. Les autres membranes renferment simultanément les deux sortes de sites. Le réticulum endoplasmique rugueux possède des sites supplémentaires au niveau des ribosomes. 相似文献17.
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