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101.
Genetic Control of Intrachromosomal Recombination in Saccharomyces Cerevisiae. I. Isolation and Genetic Characterization of Hyper-Recombination Mutations 总被引:18,自引:9,他引:9
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Eight complementation groups have been defined for recessive mutations conferring an increased mitotic intrachromosomal recombination phenotype (hpr genes) in Saccharomyces cerevisiae. Some of the mutations preferentially increase intrachromosomal gene conversion (hpr4, hpr5 and hpr8) between repeated sequences, some increase loss of a marker between duplicated genes (hpr1 and hpr6), and some increase both types of events (hpr2, hpr3 and hpr7). New alleles of the CDC2 and CDC17 genes were recovered among these mutants. The mutants were also characterized for sensitivity to DNA damaging agents and for mutator activity. Among the more interesting mutants are hpr5, which shows a biased gene conversion in a leu2-112::URA3::leu2-k duplication; and hpr1, which has a much weaker effect on interchromosomal mitotic recombination than on intrachromosomal mitotic recombination. These analyses suggest that gene conversion and reciprocal exchange can be separated mutationally. Further studies are required to show whether different recombination pathways or different outcomes of the same recombination pathway are controlled by the genes identified in this study. 相似文献
102.
All nod genes of Rhizobium meliloti are involved in alfalfa nodulation by exo mutants. 总被引:3,自引:3,他引:0
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Nodulation of alfalfa by exoB mutants of Rhizobium meliloti occurred without root hair curling or infection thread formation. nod exoB double mutants had the same nodulation deficiency as single nod mutants. Therefore, all the known nod genes are involved in nodule induction by exoB mutants, which apparently occurs via intercellular invasion. 相似文献
103.
Realization that forest decline (Waldsterben) has become an ecological crisis throughout the developed world has resulted
in massive research efforts to determine the causes of declines. It is now recognized that no single causal factor is responsible,
but that there are a variety of anthropogenic causal factor complexes interacting with natural events and processes that,
together, induce stresses in forests that culminate in declines of individual plants and of ecosystems.
It is the thesis of this article that forest declines involve all biotic and abiotic facets and parameters of forested ecosystems
and that the declines are themselves new causal factor complexes that continue to affect the stability of forested ecosystems
independently of the initial causal factor complexes. Lacking direct field or laboratory studies on these cascades of causes
and effects, this article attempts to utilize the growing body of information on plant physiological ecology to provide a
heuristic framework for evaluating long-term forest declines. 相似文献
104.
The kinetics of generation of influenza-specific cytotoxic T-lymphocyte precursor cells 总被引:2,自引:0,他引:2
A dramatic increase in the number of restimulatable (memory) cytolytic T-cell precursors (CTLps) has been demonstrated to occur 2 to 4 days postimmunization. By 4 or at the latest 6 days following in vivo priming, the frequency of restimulatable influenza-specific CTLps has reached that characteristic of a memory response. This indicates that the proliferative events which give rise to memory CTLps occur earlier than might have been expected and in fact are completed prior to the cessation of othe primary CTL response. Such information may have important significance to future immunomodulatory efforts aimed at perturbing the establishment of T-cell memory in vivo. 相似文献
105.
A K Ho T P Thomas C L Chik W B Anderson D C Klein 《The Journal of biological chemistry》1988,263(19):9292-9297
Phenylephrine is known to stimulate translocation of protein kinase C in rat pinealocytes (Sugden, D., Vanecek, J., Klein, D.C., Thomas, T.P., and Anderson, W. B. (1985) Nature 314, 359-361). In the present study, the receptor mediating this effect was found to belong to the alpha 1-adrenoceptor subclass. Activation of this receptor is also known to produce a sustained increase in [Ca2+]i by increasing net influx (Sugden, A. L., Sugden, D., and Klein, D. C. (1985) J. Biol. Chem. 261, 11608-11612), which points to the possible importance of Ca2+ influx in the subcellular redistribution (activation) of protein kinase C in intact cells. This possibility was investigated by reducing extracellular Ca2+ ((Ca2+]o) with EGTA or by inhibiting Ca2+ influx with inorganic Ca2+ blockers. These treatments reduced alpha 1-adrenoceptor-mediated translocation of protein kinase C. This suggested that elevation of Ca2+ influx alone triggers activation of protein kinase C. In support of this, it was found that treatments which elevate Ca2+ influx, including increased extracellular K+ and addition of the Ca2+ ionophore A23187, cause redistribution of protein kinase C. The effect of K+ was blocked by nifedipine and that of A23187 by EGTA, indicating that effects of these agents are Ca2+-dependent. The possible role of phospholipase C activation in these effects was examined by measuring the formation of [3H]diacylglycerol by cells labeled with [3H]arachidonic acid. Although [3H]diacylglycerol formation was easily detected in the presence or absence of an effective concentration of an inhibitor of diacylglycerol kinase, none of the agents which cause rapid translocation of protein kinase C were found to cause a rapid increase in the generation of [3H]diacylglycerol. These findings establish that an increase in Ca2+ influx is sufficient to trigger translocation of protein kinase C. In addition, we found that a very close correlation exists between translocation of protein kinase C by phenylephrine, K+, and A23187 and their ability to potentiate beta-adrenergic stimulation of cAMP and cGMP accumulation. This provides strong support to the proposal that translocation of protein kinase C is required for potentiation of beta-adrenergic stimulation of pinealocyte cAMP and cGMP accumulation. 相似文献
106.
Metabolism of leukotriene A4 into C4 by human platelets 总被引:1,自引:0,他引:1
Tritium-labelled leukotriene A4 is converted by a suspension of human platelets into leukotriene C4. The conversion is stimulated by reduced glutathione and is dependent on the platelet concentration. Formation of leukotriene C4 is temperature and time dependent and is destroyed by heating the platelets at 100 degrees C for 5 min. Verification of leukotriene C4 formation was obtained by conversion into leukotriene D4 during reaction of the HPLC-purified platelet-derived leukotriene C4 with commercial gamma-glutamyl transpeptidase. In separate experiments we incubated authentic tritiated leukotriene C4 with human platelets and we showed the formation of tritiated leukotriene D4, demonstrating the presence of gamma-glutamyl transpeptidase activity in these cells. This activity could be blocked by the presence of reduced glutathione in the incubation mixture. In contrast, erythrocytes converted tritiated leukotriene A4 almost exclusively into leukotriene B4. Although platelets have been reported to lack 5-lipoxygenase activity, our study demonstrates that platelets possess the necessary machinery to transform leukotriene A4 into leukotrienes C4 and D4. Our results suggest that an intracellular interaction between platelets and leukotriene A4-forming cells, e.g., polymorphonuclear leukocytes, could lead to the formation of these potent peptidolipids in the circulation. 相似文献
107.
Limnologic consequences of the decline in hemlock 4800 years ago in three Southern Ontario lakes 总被引:2,自引:2,他引:0
Mary M. Boucherle John P. Smol Tracie C. Oliver S. R. Brown R. McNeely 《Hydrobiologia》1986,143(1):217-225
Four thousand eight hundred years ago hemlock (Tsuga canadensis) populations were decimated throughout eastern North America. We have studied the effects of this loss from the terrestrial community on three Southern Ontario lakes: Little Round Lake, Sunfish Lake, and McKay Lake. This study includes the use of cladocerans, diatoms, chrysophytes, and bacterial pigments to assess the limnologic changes that occurred in these lakes. Each lake experienced a change in trophic status that coincided with the loss of hemlock from its catchment, but the change in the aquatic biota was different in each lake. The lakes' size may have been the most influential factor governing the response to this terrestrial disturbance. 相似文献
108.
Scanning electron microscopy was used to study the endothelial surface of the pulmonary trunk, artery, and vein in normobaric control rats as well as in rats exposed to hypobaric hypoxia for 7 and 21 days. The individual endothelial cells of the normobaric pulmonary trunk and hilar artery were flat and slightly elongated with elevated nuclear regions, and those of the intermediate-sized artery were more elongated and had more microvilli than the large arteries studied. Their endothelial cell boundaries were outlined by beaded cytoplasmic projections. The surfaces of the normobaric hilar and intermediate-sized veins were smooth and demonstrated numerous longitudinal streaks. These venous endothelial cells were elongated and their cell boundaries were outlined by low discontinuous marginal folds. Exposure to hypobaric hypoxia caused the following changes on the arterial surface: elevation of the endothelial cells; formation of microvilli-rich cell clusters; formation of hollow defects; and the attachment of leukocytes. Hypobaric hypoxia also caused the disappearance of the longitudinal streaks and the occurrence of microvilli-rich cells in the hilar veins. The endothelial surface modifications in the hypobaric rats could be related to thickening of the endothelium, intimal edema, increased intimal connective tissue, luminal invasion of leukocytes, and increased endothelial cell proliferation, known to occur in systemic arteries of hypertensive animals. 相似文献
109.
Coat color phenotype frequencies were determined in the cat population of Minneapolis and St. Paul. Mutant allele frequencies are estimated to be p (O) = 0.287, q(a) = 0.742, q(d) = 0.635, q(l) = 0.507, p(S) = 0.288. q(tb) = 0.472, p(W) = 0.016, and q(cs) = 0.214. A substantial number of cats displaying the Siamese coat pattern were found. These cats have a long history in the population. 相似文献
110.
Stomatal diffusion resistance in primary leaves of Phaseolus vulgaris L. which had been grown in light:dark cycles followed a marked circadian rhythm when the plants were transferred to continuous darkness. Reentrainment of the rhythm required more than one inductive change in photoperiod. The phasing of the rhythm of dark stomatal opening was contolled primarily by the light-on (dawn) signal, whereas the rhythm of dark closure was related to the light-off (dusk) signal. The evidence points to a dual control of the circadian clock in which a product of photosynthesis plays a major role. No evidence for phytochrome involvement in the phasing of the rhythm was found. An influence of phytochrome on the amplitude of the stomatal rhythm was observed in which removal of phytochrome-far-red absorbing form caused rapid damping. 相似文献