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941.
942.
Three-dimensional model of yeast RNA polymerase I determined by electron microscopy of two-dimensional crystals. 总被引:10,自引:3,他引:7
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Two-dimensional crystals of yeast RNA polymerase I dimers were obtained upon interaction with positively charged lipid layers. A three-dimensional surface model of the enzyme was determined by analyzing tilted crystalline areas and by taking advantage of the non-crystallographic internal symmetry of the dimer to correct for the missing viewing directions. The structure shows, at approximately 3 nm resolution, an irregularly shaped molecule 11 nm x 11 nm x 15 nm in size characterized by a 3 nm wide and 10 nm long groove which constitutes a putative DNA binding site. The overall structure is similar to the Escherichia coli holo enzyme and the yeast RNA polymerase II delta 4/7 structures. The most remarkable structural feature is a finger-shaped stalk which partially occludes the entrance of the groove and forms a 2.5 nm wide channel. We discuss the possible location of the catalytic centre and of the carboxy-terminal region of the beta-like subunit in the channel. The interference of different DNA fragments with RNA polymerase dimerization and crystallization indicates the orientation of the template in the putative DNA binding groove. 相似文献
943.
Linda I. Hannick Douglas C. Prasher Leonard W. Schultz Jeffrey R. Deschamps Keith B. Ward 《Proteins》1993,15(1):103-107
Crystals of recombinant aequorin, the photoprotein from the jellyfish Aequorea victoria, have been grown from solutions containing sodium phosphate. The crystals grow as thin plates which diffract to beyond 2.2 Å resolution. The crystals are orthorhombic, space group P21212 1; the axes are a = 89.1(1), b = 88.4(1), and c = 52.7(1) Å. The asymmetric unit contains two molecules. Crystals exposed to calcium ion solutions emit a steady glow and slowly deteriorate, confirming that the crystals consist of a charged, competent photoprotein. This represents the first successful preparation of single crystals of a photoprotein suitable for diffraction analysis. © 1993 Wiley-Liss, Inc. 相似文献
944.
Bovine parthenogenetic blastocysts following in vitro maturation and oocyte activation with ethanol 总被引:4,自引:0,他引:4
The appropriate in vitro bovine oocyte maturation and ethanol activation conditions for preimplantation bovine embryo parthenogenetic development to the blastocyst stage were investigated. A 7% ethanol concentration significantly enhanced (P<0.05) the proportion of activated, in vitro-matured bovine oocytes (7% ethanol, 83.4 +/- 3.2% versus 0% ethanol, 63.9 +/- 2.0%). The proportion of activated oocytes was significantly higher (P<0.05) by treatment with 7% ethanol for a minimum of 2 minutes (2 minutes, 89.8 +/- 4.0% versus 0.5 minutes 63.4 +/- 4.9%). Oocyte maturation for periods ranging from 30, 34, 38 and 44 hours resulted in a significant increase (P<0.05) in the proportion of activated oocytes, and in oocytes displaying 2 or 3 pronuclei versus oocytes matured for 26 hours. The proportion of cleaved, activated oocytes (2-cell stage), 4 -cell stage and parthenogenetic morula/blastocysts was significantly higher (P<0.05) within the 34-hour oocyte maturation treatment group. Although the 44-hour oocyte maturation treatment group displayed the highest proportion of activated oocytes with 2 pronuclei, it did not display the highest cleavage frequency, possibly due to the effects of postovulatory aging. Several morphologically normal parthenogenetic bovine blastocysts developed from oocytes that were in vitro matured for 34 hours. The ability to produce such parthenogenetic embryos will eventually facilitate investigation into the role(s) of the maternal and paternal genomes during bovine early development. 相似文献
945.
R. Meilan R. Horgan J. K. Heald C. E. LaMotte R. C. Schultz 《Plant Growth Regulation》1993,13(2):169-178
Zeatin-9-riboside was identified in shoots and roots of Pinus resinosa by GC-MS analysis of its permethyl derivative. Based on their chromatographic properties on Sephadex LH-20 and C18 HPLC, and their susceptibility to enzymatic degradation, several other cytokinins have been tentatively identified. The basic fraction of both the roots and shoots contained zeatin, whereas the shoots contained dihydrozeatin-O-glucoside and the roots contained zeatin-O-glucoside. Zeatin-9-riboside monophosphate, isopentenyladenosine monophosphate ([9R-5P]iP) and glucosyl phosphate derivatives were detected in the acidic fractions from both roots and shoots. There were equivalent amounts of [9R-5P]iP in both roots and shoots. The presence of equivalent amounts of [9R-5P]iP in both the roots and shots suggests that cytokinin biosynthesis may be occurring in both locations.Abbreviations AMP
adenosine-5-monophosphate
- BAP
benzylaminopurine
- BSA
bovine serum albumin
- BuOH
butan-1-ol
- CK
cytokinin
- (diH)Z
dihydrozeatin
- (diH OG)Z
dihydrozeatin-O-glucoside
- (diH OG)[9R]Z
dihydrozeatin-9-riboside-O-glucoside
- DW
dry weight
- EtOH
ethanol
- FW
fresh weight
- GC-MS
gas chromatography-mass spectrometry
- HPLC
high-performance liquid chromatography
- [9R]iP
isopentenyladenosine
- [9R-5P]iP
isopentenyladenosine monophosphate
- MeOH
methanol
- PVP
polyvinylpyrrolidone
- RFE
rotary film evaporation
- TEAB
triethyl ammonium bicarbonate
- Z
zeatin
- [9R]Z
zeatin-9-riboside
- (OG)Z
zeatin-O-glucoside
- [7G]Z
zeatin-7-glucoside
- [9R-5P]Z
zeatin-9-riboside monophosphate 相似文献
946.
Ken W. Schultz Douglas H. Cato Peter J. Corkeron M. M. Bryden 《Marine Mammal Science》1995,11(4):503-509
We present a new sound type recorded from bottlenose dolphins, Tursiops truncatus , in eastern Australian waters: low-frequency, narrow-band (LFN) harmonic sounds (defined as less than 2 kHz). Most of these sounds were of frequencies less than 1 kHz and were recorded commonly from socializing dolphins. These sounds differ significantly from narrow-band whistles, which are higher in frequency and longer in duration. The absence of these sounds in most studies of the acoustic behavior of bottlenose dolphins may reflect geographic differences in repertoires or result from insufficient sampling. Alternatively, these sounds may have been ignored where the focus of research was on other sound types. 相似文献
947.
Stephanie A. Millican Donna Schultz Meena Bagga Peter J. Coussons Karin Mü ller James V. Hunt 《Free radical research》1998,28(5):533-542
In diabetes mellitus the progression of atherosclerosis is accelerated. The interaction of glucose with athero-genic lipoproteins may be relevant to the mechanisms responsible for this vascular damage. The aim of this study was to examine the effect of glucose-modified low density lipoprotein (LDL) on human monocyte chemotaxis and to investigate the roles of oxidation and glycation in the generation of chemotactic LDL. Cu(II)-mediated LDL oxidation was potentiated by glucose in a dose-dependent manner and increased its chemotactic activity. Incubation with glucose alone, under conditions where very little oxidation was observed, also increased the chemotactic property of LDL. Neither diethylenetriamine pentaacetic acid (DETAPAC) nor aminoguanidine, which both inhibited LDL oxidation, completely inhibited the chemotactic activity of glycated oxidised LDL. The results suggest that both oxidation and glycation contribute to increased chemotactic activity. 相似文献
948.
Two distinct origins of a common BRCA1 mutation in breast-ovarian cancer families: a genetic study of 15 185delAG-mutation kindreds. 总被引:8,自引:3,他引:5
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D. B. Berman J. Wagner-Costalas D. C. Schultz H. T. Lynch M. Daly A. K. Godwin 《American journal of human genetics》1996,58(6):1166-1176
We screened 163 women from breast-ovarian cancer-prone families, as well as 178 individuals affected with breast and/or ovarian cancer but unselected for family history, for germ-line mutations in exon 2 of BRCA1, by SSCP analysis and direct sequencing. A total of 25 mutations were detected. Thirteen of 64 Jewish Ashkenazi women and 2 non-Jewish individuals were found to possess the 185delAG mutation. Haplotype data for all 15 individuals, with markers intragenic to BRCA1, suggest that the Jewish Ashkenazi individuals share a common ancestry that is distinct from the lineage shared by the other two women. These data provide the first evidence of two distinct lines of transmission for the 185delAG mutation, only one of which has its origins in the Jewish Ashkenazi population. Our screening also uncovered 10 affected individuals with an 11-bp deletion at nucleotide 188 of BRCA1 (188del11), 4 of whom are Ashkenazi Jews. This is only the third reported mutation detected within the Jewish Ashkenazi population and may represent the second most common alteration in BRCA1 found in Ashkenazi Jews in the United States. The observed overrepresentation of specific mutations within a subgroup of the general population may eventually contribute to the development of inexpensive and routine tests for BRCA1 mutations, as well as to the elucidation of other contributory factors (e.g., diet, environment, and chemical exposures) that may play a key role in cancer initiation and development. The implications of the mutational data, as well as the role that founder effect, demographic history, and penetrance play in the resulting observed phenomena, are discussed. 相似文献
949.
Tolbutamide causes open channel blockade of cystic fibrosis transmembrane conductance regulator Cl- channels. 总被引:2,自引:0,他引:2
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C J Venglarik B D Schultz A D DeRoos A K Singh R J Bridges 《Biophysical journal》1996,70(6):2696-2703
Cystic fibrosis transmembrane conductance regulator (CFTR) is an epithelial Cl- channel that is regulated by protein kinase A and cytosolic nucleotides. Previously, Sheppard and Welsh reported that the sulfonylureas glibenclamide and tolbutamide reduced CFTR whole cell currents. The aim of this study was to quantify the effects of tolbutamide on CFTR gating in excised membrane patches containing multiple channels. We chose tolbutamide because weak (i.e., fast-type) open channel blockers introduce brief events into multichannel recordings that can be readily quantified by current fluctuation analysis. Inspection of current records revealed that the addition of tolbutamide reduced the apparent single-channel current amplitude and increased the open-channel noise, as expected for a fast-type open channel blocker. The apparent decrease in unitary current amplitude provides a measure of open probability within a burst (P0 Burst), and the resulting concentration-response relationship was described by a simple Michaelis-Menten inhibition function. The concentration of tolbutamide causing a 50% reduction of Po Burst (540 +/- 20 microM) was similar to the concentration producing a 50% inhibition of short-circuit current across T84 colonic epithelial cell monolayers (400 +/- 20 microM). Changes in CFTR gating were then quantified by analyzing current fluctuations. Tolbutamide caused a high-frequency Lorentzian (corner frequency, fc > 300 Hz) to appear in the power density spectrum. The fc of this Lorentzian component increased as a linear function of tolbutamide concentration, as expected for a pseudo-first-order open-blocked mechanism and yielded estimates of the on rate (koff = 2.8 +/- 0.3 microM-1 s-1), the off rate (kon = 1210 +/- 225 s-1), and the dissociation constant (KD = 430 +/- 80 microM). Based on these observations, we propose that there is a bimolecular interaction between tolbutamide and CFTR, causing open channel blockade. 相似文献
950.
Zhe Xu Leah Lefevre Tom Ducibella Richard M. Schultz Gregory S. Kopf 《Developmental biology》1996,180(2):594
Results of numerous experiments indicate that the transient rise in intracellular Ca2+following sperm–egg fusion is essential for the subsequent events that constitute egg activation. Some events of egg activation, e.g., cortical granule exocytosis, however, appear more sensitive to intracellular Ca2+than other events, e.g., cell cycle resumption. To examine if specific events of egg activation have different thresholds for Ca2+, we manipulated buffered intracellular Ca2+concentrations by microinjecting Ca2+-BAPTA buffers and then examined the effect on the cortical granule exocytosis, recruitment of maternal mRNAs, and cell cycle resumption. We find that whereas cortical granule exocytosis occurs over a narrow threshold range of injected free Ca2+concentrations between 0.5 and 1.0 μM,recruitment of maternal mRNAs is only partially stimulated at injected free Ca2+concentrations of 2.5 μM,and no evidence for cell cycle resumption was observed (up to 2.5 μMCa2+). Although the Ca2+- and phospholipid-dependent protein kinase, protein kinase C, is implicated in aspects of egg activation, calmodulin is also a potential target for the transient increase in Ca2+that occurs following fertilization. Whereas incubation of eggs in the presence of the calmodulin antagonist W-7 followed by insemination does not block cortical granule exocytosis, cell cycle resumption, as assessed by the metaphase-to-anaphase transition, a decrease in histone H1 kinase activity and the time course for the emission of the second polar body are significantly delayed/inhibited. 相似文献