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81.
Summary The incompatibility between F plasmids is transiently suppressed in Escherichia coli strain CSH54. As a result this strain is able to maintain two F factors or an F factor and a mini-F plasmid for considerably longer periods than normal strains. When selective pressure for two markers carried by two separate Fs (or an F and mini-F) is imposed on normal strains, the two plasmids tend to form a cointegrate structure which can be detected genetically by the joint transfer of both the markers upon mating. This does not happen in CSH54; instead, the two plasmids are maintained and transferred independently. Physical evidence for the maintenance of an F and a mini-F plasmid is provided by agarose gel electrophoresis. 相似文献
82.
A purified preparation of arginine decarboxylase fromCucumis sativus seedlings displayed ornithine decarboxylase activity as well. The two decarboxylase activities associated with the single
protein responded differentially to agmatine, putrescine andPi. While agmatine was inhibitory (50 %) to arginine decarboxylase activity, ornithine decarboxylase activity was stimulated
by about 3-fold by the guanido arnine. Agmatine-stimulation of ornithine decarboxylase activity was only observed at higher
concentrations of the amine. Inorganic phosphate enhanced arginine decarboxylase activity (2-fold) but ornithine decarboxylase
activity was largely uninfluenced. Although both arginine and ornithine decarboxylase activities were inhibited by putrescine,
ornithine decarboxylase activity was profoundly curtailed even at 1 mM concentration of the diamine. The enzyme-activated
irreversible inhibitor for mammalian ornithine decarboxylase,viz. α-difluoromethyl ornithine, dramatically enhanced arginine decarboxylase activity (3–4 fold), whereas ornithine decarboxylase
activity was partially (50%) inhibited by this inhibitor. At substrate level concentrations, the decarboxylation of arginine
was not influenced by ornithine andvice-versa. Preliminary evidence for the existence of a specific inhibitor of ornithine decarboxylase activity in the crude extracts
of the plant is presented. The above results suggest that these two amino acids could be decarboxylated at two different catalytic
sites on a single protein. 相似文献
83.
Phytochemical studies on the ethanolic extracts of Caesalpinia bonduc (Fabaceae) yielded two new homoisoflavonoids, caesalpinianone, and 6-O-methylcaesalpinianone along with five known natural products, namely, hematoxylol, stereochenol A, 6′-O-acetylloganic acid, 4′-O-acetylloganic acid, and 2-O-β-d-glucosyloxy-4-methoxybenzenepropanoic acid. Structures of these compounds were elucidated with the aid of extensive NMR spectral studies. All of these compounds exhibited different levels of glutathione S-transferase (GST) inhibitory and antifungal activities. 相似文献
84.
85.
Histidine kinases have been shown to mediate responses to endogenous and exogenous stimuli in organisms such as yeast, bacteria and plants. In the model plant Arabidopsis, histidine kinases have been shown to function in hormone signaling, and abiotic and biotic stress responses. More recently, the least characterized of the Arabidopsis histidine kinases, AHK5, was demonstrated to function in resistance toward the virulent bacterium Pseudomonas syringae pv tomato DC3000 (PstDC3000) and the necrotrophic fungus Botrytis cinerea, and as a negative regulator of tolerance toward salinity. Here, we present data which indicate that AHK5 also impacts on drought stress resistance and on the outcome of an incompatible interaction with avrRpm1-expressing PstDC3000 (PstDC3000 (avrRpm1)). We present a model which proposes a role for reactive oxygen species (ROS) and hormones in integrating abiotic and biotic stress responses via AHK5. 相似文献
86.
Parent MA Goenka R Murphy E Levier K Carreiro N Golding B Ferguson G Roop RM Walker GC Baldwin CL 《Microbes and infection / Institut Pasteur》2007,9(1):55-62
The inner-membrane protein BacA affects Brucella LPS structure. A bacA deletion mutant of Brucella abortus, known as KL7 (bacA(mut)-KL7), is attenuated in BALB/c mice and protects against challenge. Thus, bacA mutation was a candidate for incorporation into live attenuated vaccines. We assessed bacA(mut)-KL7 in 2 additional mouse strains: the more resistant C57BL/6 that produces interferon-gamma throughout the infection and the highly susceptible interferon-gamma-deficient C57BL/6 in which brucellae exhibit continual exponential growth. While it was hypothesized that bacA(mut)-KL7 would exhibit even greater attenuation relative to its parent strain B. abortus 2308 in C57BL/6 mice than it did in BALB/c mice, this was not the case. Moreover, it was more pathogenic in C57BL/6 interferon-gamma-deficient mice than 2308 causing abscesses and wasting even though the splenic loads of bacA(mut)-KL7 were significantly lower. These 2 observations were correlated, respectively, with an ability of IFNgamma-activated macrophages to equivalently control strains 2308 and bacA(mut)-KL7 and the ability of bacA(mut)-KL7 organism and its LPS to induce greater amounts of pro-inflammatory cytokines than 2308. We conclude that attenuation properties of bacA mutation are dependent upon the nature of the host but more importantly that bacterial gene deletion can result in increased host pathology without an increase in bacterial load, crucial considerations for vaccine design. 相似文献
87.
How do neurons encode and store information for long periods of time? Recurring patterns of activity have been reported in various cortical structures and were suggested to play a role in information processing and memory. To study the potential role of bursts of action potentials in memory mechanisms, we investigated patterns of spontaneous multi-single-unit activity in dissociated rat cortical cultures in vitro. Spontaneous spikes were recorded from networks of approximately 50 000 neurons and glia cultured on a grid of 60 extracellular substrate- embedded electrodes (multi-electrode arrays). These networks expressed spontaneous culture- wide bursting from approximately one week in vitro. During bursts, a large portion of the active electrodes showed elevated levels of firing. Spatiotemporal activity patterns within spontaneous bursts were clustered using a correlation-based clustering algorithm, and the occurrences of these burst clusters were tracked over several hours. This analysis revealed spatiotemporally diverse bursts occurring in well-defined patterns, which remained stable for several hours. Activity evoked by strong local tetanic stimulation resulted in significant changes in the occurrences of spontaneous bursts belonging to different clusters, indicating that the dynamical flow of information in the neuronal network had been altered. The diversity of spatiotemporal structure and long-term stability of spontaneous bursts together with their plastic nature strongly suggests that such network patterns could be used as codes for information transfer and the expression of memories stored in cortical networks. 相似文献
88.
89.
Oropallo MA Held KS Goenka R Ahmad SA O'Neill PJ Steward O Lane TE Cancro MP 《Journal of immunology (Baltimore, Md. : 1950)》2012,188(11):5257-5266
Spinal cord injury (SCI) results in immune depression. To better understand how injury inhibits humoral immunity, the effects of chronic thoracic SCI on B cell development and immune responses to thymus-independent type 2 and thymus-dependent Ags were determined. Mice received complete crush injury or control laminectomy at either thoracic level 3, which disrupts descending autonomic control of the spleen, or at thoracic level 9, which conserves most splenic sympathetic activity. Although mature B cell numbers were only mildly reduced, bone marrow B cell production was transiently but profoundly depressed immediately after injury. Despite the return of normal B cell production 4 wk after SCI, mice receiving thoracic level 3 injury showed a significant reduction in their ability to mount primary thymus-independent type 2 or thymus-dependent immune responses. The latter were marked by decreases in germinal center B cells as well as class-switched high-affinity Ab-secreting cells. Importantly, injury did not affect affinity maturation per se, pre-existing B cell memory, or secondary humoral immune responses. Taken together, these findings show that chronic high thoracic SCI impairs the ability to mount optimal Ab responses to new antigenic challenges, but spares previously established humoral immunity. 相似文献
90.
N-Acyl-homoserine-lactones (AHLs) are bacterial quorum-sensing signaling molecules that regulate population density. Recent evidence demonstrates their roles in plant defense responses and root development. Hydrogen peroxide (H(2)O(2)), nitric oxide (NO), and cyclic GMP (cGMP) are essential messengers that participate in various plant physiological processes, but how these messengers modulate the plant response to N-acyl-homoserine-lactone signals remains poorly understood. Here, we show that the N-3-oxo-decanoyl-homoserine-lactone (3-O-C10-HL), in contrast to its analog with an unsubstituted branch chain at the C3 position, efficiently stimulated the formation of adventitious roots and the expression of auxin-response genes in explants of mung bean (Vigna radiata) seedlings. This response was mimicked by the exogenous application of auxin, H(2)O(2), NO, or cGMP homologs but suppressed by treatment with scavengers or inhibitors of H(2)O(2), NO, or cGMP metabolism. The 3-O-C10-HL treatment enhanced auxin basipetal transport; this effect could be reversed by treatment with H(2)O(2) or NO scavengers but not by inhibitors of cGMP synthesis. Inhibiting 3-O-C10-HL-induced H(2)O(2) or NO accumulation impaired auxin- or 3-O-C10-HL-induced cGMP synthesis; however, blocking cGMP synthesis did not affect auxin- or 3-O-C10-HL-induced H(2)O(2) or NO generation. Additionally, cGMP partially rescued the inhibitory effect of H(2)O(2) or NO scavengers on 3-O-C10-HL-induced adventitious root development and auxin-response gene expression. These results suggest that 3-O-C10-HL, unlike its analog with an unmodified branch chain at the C3 position, can accelerate auxin-dependent adventitious root formation, possibly via H(2)O(2)- and NO-dependent cGMP signaling in mung bean seedlings. 相似文献