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21.
22.
Possible structures of homopurine-homopyrimidine S1-hypersensitive sites. 总被引:31,自引:17,他引:14
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S1 nuclease hypersensitive sites in the 5' flanking regions of eukaryotic genes, present in small artificial supercoiled DNA circles, reside in homopurine-homopyrimidine stretches. The hierarchical behavior which these sites exhibit is consistent with the notion that they act as sinks of torsional free energy. By employing DMS as a single-strand-specific reagent, we show that these sites (despite their S1 sensitivity) are regions of duplex DNA. A simple thermodynamic treatment indicates that the high torsional stress in the small DNA circles is almost certain to be relieved by the formation of alternate DNA structures. The same treatment places some constraints on the types and sizes of the regions with alternate conformation. While no definitive structural conclusions can be drawn, left-handed helices seem most consistent with the extent and the pattern of sensitivity to S1 nuclease. 相似文献
23.
Photochemical production of psoralen - DNA monoadducts capable of subsequent photocrosslinking.
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Irradiation of 4' -aminomethyl-4,5' ,8-trimethyl psoralen in the presence of DNA at wavelengths between 380 and 400nm leads to efficient production of monoadducts with no significant amount of crosslinking. The yield of monoadduct attainable is high (about 35 adducts per 1000 base pairs) and can be made still higher by repeated irradiation with fresh psoralen derivative. Subsequent irradiation at 350nm results in crosslinking of a almost half of the monoattached psoralen. Studies of the yield of nonoadduct and crosslink as function of irradiation wavelength show that the action spectrum for crosslink formation is blue-shifted relative to that for monoadduct formation. 相似文献
24.
Lorraine Flaherty Linda Cantor Debra Zimmerman Dorothea Bennett 《Developmental biology》1977,59(2):237-240
Cell surface antigens of normal and anemic () mouse erythroid cells have been examined in cytotoxicity assays with two rat antisera. When tested on fetal liver cells, a rat anti-erythroblast serum recognized antigen(s) present on erythroid cells early in development, while rat anti-adult red blood cell serum recognized antigen(s) present on mature erythroid cells. Each of these sera had different activity on normal (+/+ or ) as compared to anemic () erythroid cells. 相似文献
25.
Inducer T lymphocytes synthesize and secrete peptides that stimulate growth and differentiation of many cell types, including lymphocytes and monocytes that kill foreign organisms, B lymphocytes, mast cells and hematopoietic precursor cells. To define these inducer molecules more precisely, we have generated clones of these T cells as a source of homogeneous material for biochemical analysis. These clones synthesize peptides that stimulate T and B cells to divide and that also induce the latter cells to secrete immunoglobulin. Inducer cells synthesize a 14 kilodalton growth polypeptide that stimulates T and B lymphocytes, as well as other cell types, to divide. This 14 kilodalton peptide is normally associated with different, larger peptides that appear to focus its mitogenic activity to one or another target cell. 相似文献
26.
70 S Escherichia coli ribosomes were reacted with the fluorescent dye N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulfonic acid for 10 min under mild conditions. The resulting ribosomes were fully active. 30 S subunits isolated from these particles were also fully active. They contain approximately 0.7 eq of fluorescent dye. Nearly all of it is attached to protein S18. Competitive reaction with N-ethylmaleimide implies that the fluorescent dye is located at cysteine 10 of the protein. The labeled 30 S particles will recombine with 50 S subunits to form stable 70 S particles. Thus the procedures we have developed allow the large scale preparation of an active fluorescent conjugate of the 70 S ribosome. The fluorescence of the 70 S particles is sensitive to the binding of mRNA, showing both quenching and a shift in emission spectra. Thus it affords a simple way to quantitate mRNA binding directly. In pilot studies without tRNA, the binding constant of the initiation triplet codon adenylyl-(3' leads to 5')-uridylyl-(3' leads to 5')-guanosine to 70 S ribosome was found to be an order of magnitude larger than that of polyuridylic acid. 相似文献
27.
The effects of sodium chloride concentration on the structure of chicken erythrocyte nucleosome core particles have been studied by the use of fluorescently labelled histones. Histone H3 was modified with two sulfhydryl-specific dyes and reconstituted into core nucleosomes. Between 10?4 m and 0.6 M-NaCl four different states were observed by the fluorescent techniques of collisional quenching, polarization and energy transfer. Below 5 × 10?4 m-NaCl the nucleosome is flexible, with the single cysteine residues of the two H3 species about 48 Å apart and somewhat exposed. Between 5 × 10?3 m and 10?1 m-NaCl the nucleosome is rigid and non-spherical. The cysteine residues are close together and buried. Between 10?1 m and 4 × 10?1 m-NaCl, the cysteines become slightly more exposed but remain close together. At 6 × 10?1 m-NaCl the nucleosome is very flexible. The cysteines are more than 70 Å apart and are quite exposed. The dramatic structural changes that are observed in core nucleosomes are consistent with the variety of functions in which they must participate in the cell. 相似文献
28.
We have investigated the ability of B and T lymphocyte subclasses from donor mice that produce high levels of anti-Ar antibody but have been suppressed for one idiotypic component (CRI) to induce and maintain idiotypespecific suppression. Our studies indicate: 1) Memory B cells from such mice can preempt virgin CRI+ B cells present in the host from contributing to the anti-Ar response. 2) T cells can also adoptively transfer idiotypespecific suppression. 3) B and T cells do not act synergistically in this transfer of idiotype-specific suppression. 4) Extremely small numbers of Ly23 cells transfer suppression of idiotype and most probably represent true Ts cells. 5) Ly1 cells from hyperimmune idiotypically suppressed donors can induce idiotype-specific suppression. This latter result most likely reflects the induction of idiotype-specific suppressor cells in the host. 相似文献
29.
C. H. Uittenbogaart Y. Cantor J. L. Fahey 《In vitro cellular & developmental biology. Plant》1983,19(1):67-71
Summary Human T lymphoid cell lines (MOLT-4f, MOLT-3, HSB-2, CEM) and human B lymphoid cell lines (BJAB, RAJI, WIL-2) were grown longterm
(up to 8 months) in serum-free medium. This medium consisted of Iscove's modified Dulbecco's medium (IMDM), supplemented with
bovine serum albumin (BSA) and transferrin (TF). This serum-free medium containing albumin and transferrin is designated AT-IMDM.
Lipids were not essential. Cell viability remained high, greater than 80%, in the serum-free medium and the cells maintained
their distinctive characteristics. Interleukin-2 (IL-2) production capacity was maintained by the human T lymphoid cell lines
JURKAT-77 and MO in short term culture. This simple medium composed of relatively inexpensive and readily available components
should be useful for studies of lymphoid cell growth and differentiation and lymphoid cell products.
This research was supported by a grant from the National Institutes of Health, CA 12800, and the Concern Foundation of Los
Angeles, and CA 09120 (C. U.) 相似文献
30.
Stacey L. Cantor Mark H. Zornow Leonard P. Miller Tony L. Yaksh 《Journal of neurochemistry》1992,59(5):1884-1892
We investigated the ability of N6-cyclohexyladenosine (CHA), a potent and selective agonist of the adenosine A1 receptor, to attenuate elevations of levels of extracellular hippocampal glutamate and glycine that result from episodes of transient global cerebral ischemia (TGCI). A total of 30 New Zealand white rabbits were randomly assigned to receive 0 (n = 5), 0.1 (n = 8), 1.0 (n = 6), 10 (n = 6), or 100 (n = 5) microM CHA. The drug was dissolved in artificial CSF (vehicle) and administered via a microdialysis probe placed stereotactically into the dorsal hippocampus. A second microdialysis probe placed into the contralateral hippocampus of each animal was perfused with vehicle alone. Ten minutes of TGCI was induced by neck tourniquet inflation and deliberate hypotension from 0 to 10 min. Microdialysis samples were collected as follows: every 20 min preischemia (at -80, -60, -40, -20, and 0 min); every 5 min during ischemia and in the immediate reperfusion period (at 5, 10, 15, and 20 min); and every 20 min for the remainder of the reperfusion period (at 40, 60, and 80 min). Samples were then analyzed for their concentration of glutamate and glycine by HPLC. Following 10 min of ischemia, glutamate levels increased to a peak of 3.28 +/- 0.55 times baseline and returned to preischemic levels by 40 min, i.e., during reperfusion. Glycine concentrations increased to 5.41 +/- 0.91 times over baseline and remained elevated for the duration of the study.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献