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41.
Genetic Analysis of tox+ and tox? Bacteriophages of Corynebacterium diphtheriae 总被引:18,自引:8,他引:10 下载免费PDF全文
A series of mutants derived from the temperate corynebacteriophages beta(tox+), gamma(tox-), and L(tox+) was isolated and characterized. In three-factor crosses between mutant beta phages the relative map order of the genetic markers determining extended host ranges (h and h') and loss of ability to lysogenize (c) was found to be h--c--h'. Recombination between markers was observed in matings between phage beta and the heteroimmune corynebacteriophages gamma and L. In such matings between heteroimmune phages the c markers of phages beta and gamma failed to segregate from the imm markers which determine the specificity of lysogenic immunity in these phages. The factor which directs the synthesis of diphtherial toxin during infection of appropriate corynebacterial hosts by toxinogenic corynebacteriophages is designated tox(+). It was possible to show that the tox(+) determinant of phage beta behaves as a single genetic element which occupies a position between the loci h and imm on the genetic map of this phage. Genetic recombination between mutants of phage beta occurred at very low frequencies in biparental matings performed by mixed infection of Corynebacterium diphtheriae C7(s)(-)(tox-). Considerably higher recombination frequencies were observed when lysogenic bacterial strains carrying one parental phage as prophage were induced by ultraviolet irradiation and then superinfected by the second parental phage. Maximal stimulation of genetic recombination between mutant beta phages was detected when superinfection followed ultraviolet irradiation of the lysogenic cells within a limited period of time. In matings between phages with incomplete genetic homology, the stimulation of recombination by ultraviolet radiation was much less effective. 相似文献
42.
43.
Randall S. Prather Lora J. Hagemann Neal L. First 《Molecular reproduction and development》1989,22(2):233-247
The preimplantation embryo is highly resilient to experimental manipulations. A specific manipulation that has revealed many clues to the developmental process is chimera production. Chimeras have been used to describe the importance of developmental characteristics of embryonic cells and how these characteristics are involved with developmental fate. These characteristics have been monopolized in the production of interspecific chimeras and the production of transgenic animals. This review attempts to discuss the major factors affecting preimplantation mammalian embryo chimera production. 相似文献
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45.
J C Randall D C Morris S Zeiger K Masuhara T Tsuda H C Anderson 《The journal of histochemistry and cytochemistry》1989,37(7):1069-1074
The presence and activity of alkaline phosphatase in SAOS-2 and TE-85 human osteosarcoma cells grown in culture were examined at the ultrastructural level. A monoclonal antibody raised against purified human bone osteosarcoma alkaline phosphatase was used to localize the enzyme in cultures of the osteosarcoma cells. Similar cultures were analyzed for alkaline phosphatase activity using an enzyme cytochemical method with cerium as the capture agent. Alkaline phosphatase was immunolocalized at the light microscopic level in an osteogenic sarcoma and ultrastructurally on the SAOS-2 cell membrane and the enclosing membrane of extracellular vesicular structures close to the cells. In contrast, the TE-85 cells were characterized by the absence of all but a few traces of immunolabeling at the cell surface. Enzyme cytochemical studies revealed strong alkaline phosphatase activity on the outer surface of the SAOS-2 cell membrane. Much lower enzyme activity was observed in the TE-85 cells. The results support biochemical data from previous studies and confirm that SAOS-2 cells have a significantly greater concentration of alkaline phosphatase at the plasma membrane. 相似文献
46.
The teratogenic effect of ethanol in the C57BL/6J mouse can be attenuated by pretreatment with aspirin (ASA). One prominent effect of ASA is to inhibit prostaglandin (PGE) and thromboxane (TXB2) production. We examined the effect of in vivo ethanol exposure on PGE and TXB2 production in a uterine-embryo tissue sample of C57BL/6J mice either before or after in vivo ASA pretreatment on day 10 of gestation. Ethanol increased both PGE and TXB2 production by approximately 20%. ASA caused a marked reduction of PGE and TXB2 in both control and ethanol groups by approximately 80-90%. The mouse strain, gestation time, and study parameters used in this study were the same as in the previously reported ASA attenuation of the teratogenic effect of ethanol. Therefore, the present data add additional support to the hypothesis that prostaglandin and/or thromboxane production may be involved in at least some aspects of fetal alcohol syndrome. 相似文献
47.
Identification and Characterization of Mitochondrial Acetyl-Coenzyme A Hydrolase from Pisum sativum L. Seedlings 总被引:3,自引:3,他引:0 下载免费PDF全文
Mitochondria from Pisum sativum seedlings purified free of peroxisomal and chlorophyll contamination were examined for acetyl-coenzyme A (CoA) hydrolase activity. Acetyl-CoA hydrolase activity was latent when assayed in isotonic media. The majority of the enzyme activity was found in the soluble matrix of the mitochondria. The products, acetate and CoA, were quantified by two independent methods and verified that the observed activity was an acetyl-CoA hydrolase. The pea mitochondrial acetyl-CoA hydrolase showed a Km for acetyl-CoA of 74 micromolar and a Vmax of 6.1 nanomoles per minute per milligram protein. CoA was a linear competitive inhibitor of the enzyme with a Kis of 16 micromolar. The sensitivity of the enzyme to changes in mole fraction of acetyl-CoA suggested that the changes in the intramitochondrial acetyl-CoA/CoA ratio may be an effective mechanism of control. The widespread distribution of mitochondrial acetyl-CoA hydrolase activity among different plant species indicated that this may be a general mechanism in plants for synthesizing acetate. 相似文献
48.
The effects of hydrocortisone on lung structure in fetal lambs 总被引:1,自引:0,他引:1
J Z Kendall J Lakritz C G Plopper G E Richards G C Randall M Nagamani A J Weir 《Journal of developmental physiology》1990,13(3):165-172
The effect of cortisol infusion on fetal lung development was studied in lambs. Changes were compared with those of control groups of saline-infused fetuses of the same age (day 132) and normal late gestation fetuses (142 +/- 4.6 days). Cortisol was infused into five fetal lambs at 129 days of gestation at a rate of 17.0 mg/day. Four fetuses were delivered by hysterotomy at the onset of labour-like uterine activity (58 +/- 3 h). In cortisol-infused fetuses the concentration of cortisol in fetal plasma and tracheal fluid rose to levels similar to those in normal fetuses during the last week of gestation. Progesterone concentration in maternal plasma declined at about 48 h after the start of treatment. Cortisol-infused lambs showed increases in fixed lung volume, specific lung volume, absolute volume of both parenchyma and non-parenchyma and the proportion of the parenchyma which was potential airspace and a decrease in the proportion of parenchyma. For cortisol-infused lambs Type II cell size and the abundance of lamellar bodies, and the volume fraction of cell occupied by the nucleus were similar to the 142 day group, whereas Golgi apparatus and RER were closer to age matched saline-infused (day 132) controls. Glycogen content was midway between the two control groups. We conclude that infusion of cortisol for about 60 h at physiological levels, beginning at 0.85 of gestation, accelerates many, but not all aspects of pulmonary parenchymal maturation, expressed in terms either of morphogenesis of the gas exchange area or differentiation of Type II alveolar cells. 相似文献
49.
Kathleen D. Murray Eleanor Groden Francis A. Drummond A. Randall Alford Richard H. Storch Michael D. Bentley 《Entomologia Experimentalis et Applicata》1996,80(3):503-510
The effects of citrus limonoids, applied topically to potato (Solanum tuberosum L. var. Katahdin) foliage, on Colorado potato beetle (Leptinotarsa decemlineata) (Say) (Chrysomelidae) larval development, growth, and survival were quantified in laboratory assays and a small-plot field test. In laboratory assays, survival, development rate, and body weight decreased with increasing limonoid concentration, however these measures of larval response did not significantly differ among varying periods of limonoid exposure (three, six, or nine days). Significant limonoid application concentration and frequency effects on survival, development rate, and defoliation were observed in the field test. These results indicate the potential utility of lethal and non-lethal effects of citrus limonoids for management of the Colorado potato beetle. 相似文献
50.
James M. Chen Spero Manolatos Paul W. Brandt-Rauf Randall B. Murphy Regina Monaco Matthew R. Pincus 《Journal of Protein Chemistry》1996,15(6):511-518
The three-dimensional structures of theras-p21 protein and its protein inhibitor, rap-1A, have been computed bound to theras-binding domain, RBD (residues 55–131), of theraf-p74 protein, a critical target protein ofras-p21 in theras-induced mitogenic signal transduction pathway. The coordinates of RBD have been reconstructed from the stereoview of an X-ray crystal structure of this domain bound to rap-1A and have been subjected to energy minimization. The energy-minimized structures of bothras- p21 and rap-1A, obtained in previous studies, have been docked against RBD, using the stereo figure of the RBD-rap-1A complex, based on a six-step procedure. The final energy-minimized structure of rap-1A-RBD is identical to the X-ray crystal structure. Comparison of theras-p21- and rap-1A-RBD complexes reveals differences in the structures of effector domains ofras-p21 and rap-1a, including residues 32–47, a domain that directly interacts with RBD, 60–66, 96–110, involved in the interaction ofras-p21 withjun kinase (JNK) andjun protein, and 115–126, involved in the interaction of p21 with JNK. The structure of the RBD remained the same in both complexes with the exception of small deviations in its-2 binding loop (residues 63–71) and residues 89–91, also involved in binding to rap-1A. The results suggest that the binding of these two proteins to RBD may allow them to interact with other cellular target proteins such as JNK andjun. 相似文献