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91.
Viral R plasmid Rphi6P: properties of the penicillinase plasmid prophage and the supercoiled, circular encapsidated genome.
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Properties of the viral R plasmid Rphi6P are described. As a temperate bacteriophage, it plaques on the facultative phototroph Rhodopseudomonas sphaeroides. Under aerobic conditions the phage had a latent period of 180 min, a burst time of 200 min, and a burst size of 15 to 20 particles per infective center. The encapsidated viral genome occurred as a supercoiled, circular DNA duplex with a mean contour length of 16.5 +/- 10 micron. Percent guanine plus cytosine, as calculated from thermal denaturation profiles, was 63.5. Mitomycin C-induced loss of the prophage suggested an extrachromosomal location in the host cell. Use of this curing agent enabled the isolation of a plasmid-free strain of R. sphaeroides. Biophysical analysis of the plasmid-free strain lysogenized with Rphi6P confirmed that the prophage occurred as a plasmid in the host cell. 相似文献
92.
S Z Ben-Sasson M F Lipscomb T F Tucker J W Uhr 《Journal of immunology (Baltimore, Md. : 1950)》1978,120(6):1902-1906
Peritoneal exudate lymphocytes (PEL) from immune guinea pigs that adhere to antigen-pulsed macrophages (MO) were cultured for 1 week to yield a population enriched in antigen-specific (selected) T cells. These cells bind specifically within hours to fresh autologous antigen-pulsed MO. Thd dissociation of these selected PEL from antigen-pulsed MO was studied. No evidence was obtained that factors in the culture medium play a role in dissociation. Lymphocytes that have dissociated from antigen-pulsed MO are usually fully capable of rebinding to MO freshly pulsed with antigen, suggesting that there is no deficiency in the lymphocytes ability to bind. In contrast, readding antigen to cultures during incubation prevents the predicted dissociation. Moreover, repulsing MO cultured without selected PEL restores their capacity to bind fresh selected PEL. These findings indicate that decay of antigen associated with with MO is the major mechanism underlying the observed dissociation. 相似文献
93.
Essential oils were eamined in nine clones of Mentha arvensis, four clones of M. spicata, and 20 clones of M. gracilis. An F1 hybrid of M. arvensis M. spicata, selected on the basis of morphology and chromosome number, was matched with one clone of M. Gracilis. Genes for the inheritance of limonene, 1,8-cineole, linalool, isomenthone, carvone, and piperitenone oide were identified in one clone of M. arvensis and two clones of M. spicata. The range of essential oil compounds detected indicates that no one character can be used to identify M. gracilis, but the critical compounds of the oil of M. gracilis can be derived from crosses of M. arvensis M. spicata. 相似文献
94.
J R Merwin A Tucker L Madisen A Purchio J Madri 《Biochemical and biophysical research communications》1991,175(2):589-595
Functional biological assays were performed using a hybrid molecule of Transforming Growth Factor-Beta (TGF-5 beta) where nine amino acids near the cleavage site of TGF-beta 1 were substituted with nine amino acids located in the identical position of TGF-beta 2. Bovine aortic endothelial and smooth muscle cells as well as rat epididymal fat pad microvascular endothelia were studied in three distinct bioassays examining proliferation, migration and angiogenesis. The data suggested TGF-5 beta elicited results that do not differ significantly from the TGF-beta 1 isoform, while TGF-beta 2 expressed unique characteristics. We have also shown that these amino acid substitutions to TGF-beta 1 do not, in fact, alter the biological functions of the growth factor. 相似文献
95.
Employing nine clones ofMentha arvensis and four clones ofM. spicata, 932 F, hybrids were synthesized and compared to 20 clones ofM. x gracilis. Two clones ofM. x gracilis with 60 somatic chromosomes were matched to a selected F1 hybrid. The other 18 clones ofM. x gracilis had somatic chromosome numbers of 60, 72, 84, and 96, and while these chromosome numbers appeared in the F1 progeny, morphological matches correlated with their correct chromosome numbers were not synthesized. The range of pollen and seed fertility, as well as the inheritance of male-sterility, leaf pubescence, and crispness, indicates that no one character can be used to identifyM. x gracilis, but all characters can be explained fromM. arvensis x M. spicata. 相似文献
96.
Synthetic leukotrienes (LT) C4 and D4 elicited concentration-dependent contractions of the guinea pig uterus between 10?8-10?6M, whereas LTE4 appeared 1000-fold weaker. The potencies of LTC4 and LTD4 were similar to that of acetylcholine and PGF2α but weaker than that of PGE2. The maximal contractions elicited by LTC4 and LTD4 were 66.0 ± 2.1% and 63.8 ± 4.6% that elicited by acetylcholine. FPL 55712 (10?5M) antagonized the uterine contractile activity of LTD4, while meclofenamic acid at 10?5M but not at 10?6M also antagonized the LTD4-induced contration. Radioimmunoassay of the uterine tissue bathing fluid following LTD4 indicated the variable presence of low concentrations of PGE2, PGF2α and TXB2. These results demonstrate the LTC4 and LTD4 possess significant uterine contractile activity, which may only partially be mediated indirectly via prostaglandin products. 相似文献
97.
Anthony V. Capuco Pamela A. Feldhoff R.Michael Akers James L. Wittliff H.Allen Tucker 《Steroids》1982,40(5):503-517
Binding of [3H]R5020 (17,21-dimethyl-19-nor-4,9-pregnadiene-3, 20-dione) to bovine mammary cytosol indicated the presence of progestin binding sites of high-affinity and low-capacity in tissue from prepartum, nonlactating and from postpartum, lactating cows. To prevent binding of [3H]R5020 to glucocorticoid binding sites, a 200-fold molar excess of nonradioactive cortisol was included during all incubations, thus specific binding was limited to progestin binding sites. Nonradioactive R5020 and progesterone effectively inhibited [3H]R5020 binding to progestin binding sites, while estradiol-17β, dihydrotestosterone (17β-hydroxy-5α-androstan-3-one), dexamethasone (9-fluoro-11β, 17, 21-trihydroxy-16α-methyl-1,4-pregnadiene-3,20-dione) or additional cortisol were ineffective. Dissociation constants for specifically bound [3H]R5020 in cytosol from mammary tissue of nonlactating and lactating cows were nearly identical, averaging 1.9 ( ± 0.3) and 0.8( ± 0.2) × 10?9M, respectively. However, binding capacities (fmol/mg cytosolic protein) were greater in cytosol from prepartum, nonlactating (179 ± 53) than postpartum, lactating (41 ± 15) cows. Specific binding components in cytosol from lactating cows sedimented in the 6-7S region on linear sucrose density gradients. When subjected to isoelectric focusing, specific binders with isoelectric points (pI) of approximately 6.1, 7.9 and 8.3 were resolved. The decrease in number of binding sites during lactation was due to the virtual absence of the anionic binding species, suggesting that their presence is necessary for progesterone to inhibit milk secretion. 相似文献
98.
99.
Craig S. Tucker 《Hydrobiologia》1981,85(1):73-76
Eichhornia crassipes (Mart.) Solms, Pistia stratiotes (L.), and Lemna minor (L.) were cultured at four different densities each and analyzed for cell-wall fraction, crude protein, total available carbohydrate and ash. Cell-wall fraction increased and crude protein content decreased as density increased in Eichhornia and Pistia cultures. The cell-wall and crude protein content of Lemna did not change with increasing culture density. Differences in the trends of cell-wall and crude protein content of the three plants at increasing culture densities appear to be related to differences in growth form. There was no difference in the total available carbohydrate or ash content of the three species at different culture densities. 相似文献
100.
Transformation of Rhodopseudomonas sphaeroides with deoxyribonucleic acid isolated from bacteriophage R phi 6P. 总被引:2,自引:2,他引:0
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The transformation of the photosynthetic bacterium Rhodopseudomonas sphaeroides with the circular genome of the penicillinase-encoding, temperate bacteriophage R phi 6P was demonstrated. The transformation was dependent on the infection of the recipient by another, apparently closely related, temperature bacteriophage, R phi 9. Optimum transformation occurred in the recipient cells already lysogenic for R phi 9 when superinfected with that bacteriophage at multiplicities of infection between 1 and 10 R phi 9 particles per recipient cell. 相似文献