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101.
S Molineaux  J E Clements 《Gene》1983,23(2):137-148
Visna viral DNA, like other retroviral DNA, exists in two circular forms in infected cells. The larger probably contains two copies of the LTR, the smaller, one copy. Recombinant DNA techniques were used to clone unintegrated circular visna viral DNA in the lambda WES . lambda B vector. Circular visna viral DNA was digested with the restriction enzyme SstI, which yields a 9.2-kb viral DNA fragment containing 90% of the viral genome colinear with the restriction map of linear viral DNA. This fragment extends from a site about 900 bp from the left (5') end of the viral DNA molecule, through the 3' region, including U3 and R sequences at its right (3') end. The recombinant clones isolated contain visna viral DNA inserts which range in size from 3.1 kb to 9.2 kb. All the clones contain the 5' region intact, but most had sustained deletions of varying lengths in the 3' terminal region of the cloned fragment.  相似文献   
102.
The influence of five different N-terminal protecting groups (For, Ac, Boc, Z, and Fmoc) and reaction conditions (temperature and dimethylformamide content) on the alpha-chymotrypsin-catalyzed synthesis of the dipeptide derivative X-Phe-Leu-NH(2) was studied. Groups such as For, Ac, Boc, and Z always rendered good peptide yields (82% to 85%) at low reaction temperatures and DMF concentrations, which depended on the N-alpha protection choice. Boc and Z were the most reactive N-alpha groups and, in addition, the most suitable for peptide synthesis. On the other hand, the use of empirical design methodologies allowed, with minimal experimentation and by multiple regression, to deduce an equation, which correlates the logarithm of the first order kinetic constant (log k') with reaction temperature, DMF concentration, and hydrophobicity (log P values) of the different protecting groups. The predictive value of the equation was tested by comparing the performance of another protective group, such as Aloc, with the performance predicted by said equation. Experimental and calculated k' values were found to be in good agreement.  相似文献   
103.
A new parameter, the relative utilization of tricarboxylic acid (TCA) cycle beta, is introduced to quantitatively account for the involvement of fermentation pathways and TCA cycle in the utilization of oxygen under oxygen-limiting (microaerobic) conditions. With the facultative anaerobe Enterobacter aerogenes, which produces 2,3-butanediol, a method is proposed to calculate beta from measurement of metabolites and exhaust gas. In continuous culture beta was found to be small under oxygen limitation, indicating that the fermentation pathways were preferred over the TCA cycle and oxygen was almost entirely consumed through oxidation of reduced nicotinamide adenine dinucleotide (NADH(2)) released by fermentation under these conditions. The increase of beta at high oxygen supply revealed a saturation of oxygen utilization through fermentation pathways. It could be concluded that, for the optimal performance of a microaerobic culture, oxygen uptake rate must be kept at such a level that as much NADH(2) as possible from fermentation pathways is oxidized by oxygen, and at the same time the utilization of TCA cycle is kept at a minimum. As the dynamics of the microaerobic culture can be fast, a significant effect of reactor hydrodynamics, i.e., mixing, on the overall performance can be expected. This was confirmed experimentally, and the parameter beta proved to be a useful reactor design criterium for the microaerobic cultivation. (c) 1992 John Wiley & Sons, Inc.  相似文献   
104.
105.
Summary Glucan formation ofSchizophyllum commune andSclerotium glucanicum were investigated. Process data obtained during batch cultivation are presented. Glucan release can be improved by oxygen limitation. Thus, growth and glucan release are influenced by oxygen in opposite ways. Possible pathways of this oxygen-dependent regulation are discussed. A draft-tube/propeller system, rushtonturbine-, fan- and helicon-ribbon-impeller as well as a fundaspi and intermig agitator were tested. The 4-bladed fan impeller withd *=0.64 yielded the best results, since effective bulk mixing is much more important than bubble break up (micromixing) with regard to this system. Fed-batch cultivation always resulted in higher rates of glucan formation than the batch process.  相似文献   
106.
Summary A central composite design (CCD) was used to evaluate, for the purpose of future process optimization, the influence of pH, yeast extract and ammonium chloride concentrations on the proportion of periplasmic hepatitisB pre-S2 antigen in the recombinant yeastHansenula polymorpha. Each factor was tested at five levels, and a second order polynomial model for the proportion of periplasmic antigen was fitted to the treatment combinations. pH showed the greatest effect: the proportion of periplasmic antigen was greatly increased at the higher pH levels. At the higher pH levels used, the proportion of periplasmic antigen was enhanced by a high concentration of ammonium chloride. Additional experiments have confirmed both the validity of the selected model and the optimal conditions found. A significant correlation was found between the proportion of periplasmic antigen and the total yield of antigen. These results indicated that is should be possible to modulate the distribution of the pre-S2 antigen between the periplasm and the cytoplasm of the yeast.  相似文献   
107.
We report here about an antigen that is expressed in the central nervous system (CNS) of Drosophila only during the embryonic and metamorphic stages. In Drosophila, axonogenesis and synaptogenesis occur twice during the development: first in the embryonic and second in the metamorphic stages. We generated monoclonal antibodies (MAbs) in order to obtain molecular probes for analyzing axonogenesis or synaptogenesis in the CNS on the assumption that good candidates for molecules responsible for such phenomena must be present in the neuropil during those stages exclusively. As a result, we found MAb 66B2 whose intense immunoreactivity in the neuropil of the CNS was observed exclusively in the embryo and pupa, and not in the larva and adult. Immunoblot analyses showed that MAb 66B2 binds specifically to a protein with an apparent molecular weight of 350 K and neutral pl in the prepupal CNS. A significant amount of the antigen was isolated in forms that were soluble without detergent. Results of immunohistochemistry with MAb 66B2 in a primary culture of embryos showed that some live cells in the ganglion-like cluster were stained, and that neuronal cell bodies and neurites emanating from there were negative. These results strongly suggest that the 66B2 antigen observed in the CNS is an extracellular matrix component secreted from nonneuronal cells. These developmental changes in the 66B2 immuno-reactivity in the CNS presumably reflect dynamic changes of an extracellular matrix in the CNS that are accompanied by axonogenesis or synaptogenesis. © 1992 John Wiley & Sons, Inc.  相似文献   
108.
The susceptibility of sorghum to the shoot fly Atherigona soccata Rondani, (Diptera: Muscidae) is affected by seedling age and is highest when seedlings are 8–12 days old. This corresponds with high moisture accumulation on the central leaf which is the path of newly hatched larva as it moves downwards from the oviposition site, towards the growing apex. Studies showed that leaf surface wetness (LSW) of the central shoot leaf was higher in 10-day old seedlings than in seedlings of other ages. Similarly, LSW was much higher in the susceptible sorghum genotype CSH 1 than in the resistant genotype IS 2146. Larvae moved faster towards the growing point and produced deadhearts much earlier in CSH 1 than in IS 2146. They also moved faster in 10-day old seedlings than in seedlings of other ages. It was also shown that the leaf surface wetness of the central shoot leaf is a more reliable parameter of resistance than the glossy leaf trait or trichome density.
L'influence de la humidité de la surface foliaire sur le comportement de la mouche des pousses du sorgho
Résumé La sensibilité du sorgho à la mouche des pousses du sorgho, Atherigona soccata Rondani, est liée à l'âge de la plantule. Elle est plus forte lorsque la plantule est âgée de 8 à 12 jours et la sensibilité est maximale à 10 jours. A ce stade de croissance on observe une forte accumulation d'humidité sur la feuille centrale de la tige. Les jeunes larves traversent cette zone humide lorsqu'elles descendent vers la zone de croissance à partir des pontes déposées sur la face ventrale des feuilles déroulées.Des études ont été menées à l'ICRISAT (Inde) sur la relation entre l'humidité de la feuille centrale de la tige des plantules du sorgho et les dégâts provoqués par la mouche des pousses. L'humidité de la surface des feuilles (HSF) a été estimée grâce à une échelle visuelle graduée 1 à 5 où, 1 = pas d'humidité apparente et 5 = surface de la feuille recouverte de gouttes d'eau. La HSF est plus élevée sur des pousses de sorgho âgées de 10 j que sur les pousses appartenant à d'autres classes d'âge. Les valeurs observées sont également plus fortes pour les variétés non résistantes à ce ravageur (CSH 1,4.8) que pour les variétés résistantes (IS 2146, (2)). La vitesse du déplacement larvaire entre le cornet et la zone de la croissance varie en fonction de l'âge de la plante et des cultivars. Les larves migrent plus rapidement vers la zone de croissance et provoquent la mort du coeur du sorgho plus tôt dans la variété CSH 1 que dans IS 2146. Les larves se déplacent plus rapidement dans les pousses âgées de 10 j que dans les pousses appartenant à d'autres classes d'âge.Des études ont également démontré que la HSF n'est pas directement liée au caractère feuille lisse où à la densité des trichomes. La HSF est faible pour les génotypes résistants présentent où non le caractère feuille lisse. Par contre la HSF est élevée pour les génotypes non résistants présentant le caractère feuille lisse ou non. Aucune relation directe entre la densité des trichomes et les dégâts provoqués par la mouche des pousses n'a pu être mise en évidence. L'analyse des correlations établie pour les caractères de surface des feuilles avec la mort du cur des sorghos indique que les correlations sont faibles et non-significatives pour le caractère feuille lisse (0.49) et la densité des trichomes (0.39 et 0.2). Par contre les correlations sont fortes et significatives pour la HSF (0.82).On conclue que la HSF de la feuille centrale de la tige est un facteur important dans le déterminisme de la résistance du sorgho vis à vis de la mouche des pousses. Les relations entre les processus physiologiques de la plante et les facteurs impliquées dans l'accumulation d'eau sur la surface des feuilles font actuellement l'objet d'études détaillées.
  相似文献   
109.
The spindle apparatus ofCoprinus micaceus begins to develop from the diglobular polar body outside the nucleus. During both meiotic divisions it operates inside the nuclear envelope and consists of two amorphous poles, a central bundle of interpolar microtubules, and chromosomal microtubules. A metaphase plate cannot exist because the interpolar strand of fibers is persistent throughout the division process. Within the spindle axis more than 100 microtubules can be estimated. They are encircled by a ring of chromatic structures. During the telophase the former spindle pole is evaginated from the nuclear envelope and contacts the plasmalemma near the cell wall.  相似文献   
110.
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