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91.
Plasmid rolling circle replication and its control 总被引:10,自引:0,他引:10
Manuel Espinosa Gloria del Solar Fernando Rojo Juan C. Alonso 《FEMS microbiology letters》1995,130(2-3):111-120
Abstract This review summarises current information on rolling circle replicating plasmids originally isolated from Gram-positive bacteria with a low guanine and cytosine content in their DNA. It focuses on the peculiar biological features of these small, high copy number plasmids that replicate via an asymmetric RC mechanism. The regulation of plasmid copy number is also discussed. 相似文献
92.
Gonzalo Bonelo Manuel Megías Dr. Antonio Ventosa Joaquín J. Nieto Francisco Ruiz-Berraquero 《Current microbiology》1984,11(3):165-169
Compared withEscherichia coli, Halobacterium mediterranei was highly resistant to the lethal effect of N-methyl-N-nitro-N-nitrosoguanidine (nitrosoguanidine), but it was sensitive to the mutagenic action of this chemical agent. Nitrosoguanidine at 500 g ml–1 gave a cell survival level between 1% and 10%, and this allowed us to obtain more Josamycin-resistant mutants compared with lower concentrations, which gave higher survival rates but fewer mutants. The efficiency of the mutagenicity obtained with the nitrosoguanidine treatment was examined under a variety of conditions. The optimal conditions for obtaining Josamycinresistant mutants were achieved by exposing, in darkness and without shaking, a suspension of about 108 log-phase cells to 500 g nitrosoguanidine in 1 ml of 50 mM modified saline Tris-maleate buffer at pH 7.5, or in 1 ml of 5 mM modified saline Tris-citrate-maleate for 30 min at 37°C. 相似文献
93.
94.
The incorporation of3H-thymidine into DNA in the brains of the 17-day and 20-day old rat fetuses was significantly reduced by maternal zinc restriction
during pregnancy. The activity of the enzyme thymidine kinase (EC 2.7.1.21) was similarly reduced in the zine-deprived fetal
brains on days 14 and 20 of gestation, but not on day 17. Fetal brain alkaline phosphatase (EC 3.1.3.1) was significantly
depressed by maternal zinc deprivation on days 17 and 20 of pregnancy.
The data suggest an association between thymidine kinase and the reduced incorporation of3H-thymidine into DNA in the brains of 20-day old fetuses but not in animals on day 17. Alkaline phosphatase was however depressed
at this stage.
The suggestion is made that because of the complexity of brain development, future biochemical studies in this area should
concern specific structures in the brain at particular critical stages during neurogenesis. 相似文献
95.
96.
Tissue biopsies from (1) some chronic inflammatory diseases, (2) a necrotic tumoral process, (3) normal human lymphatic ganglia, and (4) two congenital diseases of the adrenal cortex were selected for study. A block from each biopsy was fixed in glutaraldehyde-paraformaldehyde; a second block was fixed in 10% formaldehyde. In all cases septate junctions between digestive vacuoles did occur in phagocytic cells and some adrenal cortex cells fixed in formaldehyde. These junctions were similar to those reported recently for malakoplakia phagocytes. Consistently, they were not found to attach organelles other than lysosomes derivatives. Both phagocytes and adrenal cortex cells in the material fixed in glutaraldehyde-paraformaldehyde did not display adhesive specializations between digestive vacuoles. This suggests that the septate junctions described herein are artifactuous structures induced by formaldehyde. There is, however, a certain degree of specificity of cells having the capability of developing these septate junctions. It is assumed that the coating material of digestive organelles in phogocytes and some other cells would be responsible for both cell specificity and organelle specificity of the formaldehyde-induced septate junctions. 相似文献
97.
98.
G C Whittow C A Scammell J K Manuel D Rand M Leong 《Archives internationales de physiologie et de biochimie》1977,85(1):139-151
Six slow loris were exposed to air temperatures between 10 degrees C and 40 degrees C. Rectal temperature was stable (mean, 34.8 degrees C) at air temperatures between 17 degrees C and 31 degrees C; at higher air temperatures, the animals became hyperthermic. Oxygen consumption was minimal at air temperatures of 31.4-36.6 degrees C; the mean value (0.250 ml O2 g-1 h-1) was only 36% of the expected level for a eutherian Mammal. The slow loris increased its heat production at lower air temperatures. Thermal polypnea occurred in response to heat, and some of the animals were able to dissipate their entire metabolic heat production at lower air temperatures. Thermal polypnea occurred in response to heat, and some of the animals were able the combined thermal conductance of the tissues and haircoat was 73% of the predicted values. It was concluded that, in spite of its low metabolic rate, the slow loris had effective responses to moderate cold, and that, in addition, it was well adapted to a hot climate. 相似文献
99.
100.
Differential proliferative response of cultured fetal and regenerating hepatocytes to growth factors and hormones 总被引:5,自引:0,他引:5
Carmen de Juan Manuel Benito Alberto Alvarez Isabel Fabregat 《Experimental cell research》1992,202(2):495-500
Upon epidermal growth factor (EGF) stimulation, fetal (20 days of gestation) and regenerating (44-48 h after partial hepatectomy) rat hepatocytes, isolated and cultured under identical conditions, increased DNA synthesis and entered into S-phase and mitosis, measured as [3H]thymidine incorporation and DNA content per nucleus in a flow cytometer, respectively. Fetal hepatocytes consisted of a homogeneous population of diploid (2C) cells. Two different populations of cells were present in regenerating liver, diploid (2C) and tetraploid (4C) cells, that responded to EGF. Glucagon or norepinephrine did not affect EGF stimulation of DNA synthesis in fetal liver cells, but they potentiated EGF response in regenerating hepatocyte cultures. Glucocorticoid hormones (dexamethasone) inhibited DNA synthesis in fetal hepatocyte cultures, an effect potentiated by the presence of glucagon or norepinephrine. In contrast, in regenerating hepatocytes, dexamethasone increased EGF-induced proliferation. EGF-dependent DNA synthesis was inhibited by TGF-beta in both fetal and regenerating cultured hepatocytes. TGF-beta action was partially suppressed by norepinephrine in regenerating hepatocytes, but was without effect in fetal hepatocyte cultures, whereas a synergistic action between TGF-beta and dexamethasone inhibiting growth in fetal but not in regenerating hepatocytes was found. Taken together, these results may suggest that there are significant differences between fetal and regenerating hepatocyte growth in their response to various hormones. 相似文献