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61.
Mark L. Carpenter Sarah A. Cassidy Keith R. Fox 《Journal of molecular recognition : JMR》1994,7(3):189-197
We have studied the interaction of the GC-specific, minor groove-binding ligand, mithramycin, with cloned DNA inserts containing isolated GC and CG sites flanked by regions of (AT)n and An · Tn using DNase I and hydroxyl radical footprinting. We find that mithramycin binds to GC better than CG and that AGCT is a better site than TGCA. Sites flanked by (AT)n appear to be bound better than those surrounded by An · Tn. Although no footprints are produced at T9GCA9 and T15CGA15, DNase I cleavage is enhanced with the GC sites suggesting that there is some interaction with the ligand. Mithramycin also alters the DNase I cleavage of (GA)n · (CT)n. 相似文献
62.
The trait for somatic embryogenesis is being introduced sexually into alfalfa (Medicago sativa) breeding populations to facilitate genetic transformation of this crop. Cocultivation experiments were conducted with an agronomically-improved embryogenic clone from one such population as well as with two other embryogenic clones, one of which was the source of the embryogenic trait in the breeding populations. Transgenic plants were produced from the agronomically-improved clone whereas none were produced from the other two clones. Among the 16 transgenic plants analyzed there was a range in both copy number and number of integration sites for the NPT-II gene; those plants regenerated after a prolonged selection phase in vitro generally had the highest numbers in both respects. There was no evidence of sectoral chimerism of the transgene in a subsample of transgenic plants analyzed by PCR. 相似文献
63.
The fluorescent dye FM1-43 has been used to indicate membrane changes in individual bovine anterior pituitary cells exposed to secretory stimuli. After ten minutes incubation with FM1-43 (2 M), cells showed three patterns of dye fluorescence: annular, partly filled and uniformly filled. FM1-43 fluorescence was increased in 61% of the cells by TRH (40 nM), a physiological stimulus for prolactin secretion, and in 89% of the cells by 60 mM external K+. The fluorescence also increased when cells incubated in the presence of quinpirole, a dopamine D2-receptor agonist which inhibits prolactin secretion, were exposed to raclopride, a D-2 antagonist. The increases in FM1-43 fluorescence caused by these treatments suggests that the dye acts as an indicator of secretion, possibly through incorporation into secretory vesicle membranes exposed on the cell surface during exocytosis. If the dye was washed away after loading, the fluorescence of partly and uniformly filled cells was retained and a rise in fluorescence could still be seen on stimulation by TRH. This suggests that some dye had been taken up by endocytosis and trapped in an intracellular compartment, which expanded through membrane recapture after TRH stimulation. FM1-43 could therefore be a useful probe for membrane cycling associated with secretory responses. 相似文献
64.
Sarah Grant Andreas Houben Boris Vyskot Jiri Siroky Wei-Hua Pan Jiri Macas Heinz Saedler 《Genesis (New York, N.Y. : 2000)》1994,15(3):214-230
Most flowering plant species are hermaphroditic, but a small number of species in most plant families are unisexual (i.e., an individ-ual will produce only male or female gametes). Because species with unisexual flowers have evolved repeatedly from hermaphroditic progenitors, the mechanisms controlling sex determination in flowering plants are extremely diverse. Sex is most strongly determined by genotype in all species but the mechanisms range from a single controlling locus to sex chromosomes bearing several linked locirequired for sex determination. Plant hormones also influence sex expression with variable effects from species to species. Here, we review the genetic control of sex determination from a number of plant species to illustrate the variety of extant mechanisms. We emphasize species that are now used as models to investigate the molecular biology of sex determination. We also present our own investigations of the structure of plant sex chromosomes of white campion (Silene latifolia - Melan-drium album). The cytogenetic basis of sex determination in white campion is similar to mammals in that it has a male-specific Y-chromosome that carries dominant male determining genes. If one copy of this chromosome is in the genome, the plant is male. Otherwise it is female. Like mammalian Y-chromosomes, the white campion Y-chromosome is rich in repetitive DNA. We isolated repetitive sequences from microdissected Y-chromosomes of white campion to study the distribution of homologous repeated sequences on the Y-chromosome and the other chromosomes. We found the Y to be especially rich in repetitive sequences that were generally dispersed over all the white campion chromosomes. Despite its repetitive character, the Y-chromosome is mainly euchromatic. This may be due to the relatively recent evolution of the white campion sex chromosomes compared to the sex chromosomes of animals. © 1994 Wiley-Liss, Inc. 相似文献
65.
Abstract: The N-methyl-d -aspartate (NMDA) receptor possesses two distinct amino acid recognition sites, one for glutamate and one for glycine, which appear to be allosterically linked. Using rat cortex/hippocampus P2 membranes we have investigated the effect of glutamate recognition site ligands on [3H]glycine (agonist) and (±)4-trans-2-car-boxy-5,7-dichloro-4-[3H]phenylaminocarbonylamino-1,2,3,4-tetrahydroquinoline ([3H]l -689,560; antagonist) binding to the glycine site and the effect of glycine recognition site ligands on l -[3H]glutamate (agonist), dl -3-(2-carboxypiperazin-4-yl)-[3H]propyl-1 -phosphonate ([3H]-CPP; “C-7” antagonist), and cis-4-phosphonomethyl-2-[3H]piperidine carboxylate ([3H]CGS-19755; “C-5” antagonist) binding to the glutamate site. “C-7” glutamate site antagonists partially inhibited [3H]l -689,560 binding but had no effect on [3H]glycine binding, whereas “C-5” antagonists partially inhibited the binding of both radioligands. Glycine, d -serine, and d -cycloserine partially inhibited [3H]CGS-19755 binding but had little effect on l -[3H]-glutamate or [3H]CPP binding, whereas the partial agonists (+)-3-amino-1-hydroxypyrrolid-2-one [(+)-HA-966], 3R-(+)cis-4-methyl-HA-966 (l -687,414), and 1-amino-1-carboxycyclobutane all enhanced [3H]CPP binding but had no effect on [3H]CGS-19755 binding, and (+)-HA-966 and l -687,414 inhibited l -[3H]glutamate binding. The association and dissociation rates of [3H]l -689,560 binding were decreased by CPP and d -2-amino-5-phosphonopentanoic acid (“C-5”). Saturation analysis of [3H]l -689,560 binding carried out at equilibrium showed that CPP had little effect on the affinity or number of [3H]l -689,560 binding sites. These results indicate that complex interactions occur between the glutamate and glycine recognition sites on the NMDA receptor. In addition, mechanisms other than allosterism may underlie some effects, and the possibility of a steric interaction between CPP and [3H]l -689,560 is discussed. 相似文献
66.
Hydrobiologia - In 1988–89 a 200 m core was drilled down to granite bedrock in the Pretoria Saltpan as part of a project to ascertain the origin of this unusual feature. The top 90 m of the... 相似文献
67.
In the cyanobacterium Synechococcus UTEX 625, the extent of expression of carboxysomes appeared dependent on the level of inorganic carbon (CO2+HCO
inf3
sup-
) in the growth medium. In cells grown under 5% CO2 and in those bubbled with air, carboxysomes were present in low numbers (<2 · longitudinal section-1) and were distributed in an apparently random manner throughout the centroplasm. In contrast, cells grown in standing culture and those bubbled with 30 l CO2 · 1-1 possessed many carboxysomes (>8 · longitudinal section-1). Moreover, carboxysomes in these cells were usually positioned near the cell periphery, aligned along the interface between the centroplasm and the photosynthetic thylakoids. This arrangement of carboxysomes coincided with the full induction of the HCO
inf3
sup-
transport system that is involved in concentrating inorganic carbon within the cells for subsequent use in photosynthesis. Immunolocalization studies indicate that the Calvin cycle enzyme ribulose bisphosphate carboxylase was predominantly carboxysome-localized, regardless of the inorganic carbon concentration of the growth medium, while phosphoribulokinase was confined to the thylakoid region. It is postulated that the peripheral arrangement of carboxysomes may provide for more efficient photosynthetic utilization of the internal inorganic carbon pool in cells from cultures where carbon resources are limiting.Abbreviations Chl
chlorophyll
- DIC
dissolved inorganic carbon (CO2+HCO
inf3
sup-
+CO
inf3
sup2-
)
- PRK
phosphoribulokinase
- RuBP
ribulose 1,5-bisphosphate
- Rubisco LS
large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase 相似文献
68.
E. Stephen Buescher Sarah M. McIlheran Steven M. Banks Andrezej P. Kudelka John J. Kavanagh Saroj Vadhan-Raj 《Cancer immunology, immunotherapy : CII》1993,37(1):26-30
During a phase I trial of interleukin-1 (IL-1) in patients with ovarian carcinomas, the effects of this treatment on blood granulocyte respiratory burst and locomotive responses were examined. Differences in baseline granulocyte function in patients as well as dose-related effects of IL-1 treatment were observed. Patients enrolled early in the trial (low-dose patients) had significantly lower locomotive responses before treatment than their paired controls; these low responses normalized after 5 days of continuous-infusion IL-1 treatment. Patients enrolled later (high-dose patients) had normal locomotive responses before treatment and IL-1 treatment was associated with suppression of responses to selected stimuli at the end of treatment. Pretreatment respiratory burst responses in both low-and high-dose patient groups were essentially normal, but the rates of granulocyte H2O2 production following phorbol myristate acetate stimulation became significantly less than control values at the end of treatment. In vitro exposure of either patient or control cells to 150 U/ml IL-1 did not alter their locomotive or respiratory burst responses, suggesting the observed in vivo effects were not mediated directly by IL-1. Treatment with IL-1 is associated with changes in ex vivo granulocyte function that are related to the IL-1 dose. Treatment with low doses of IL-1 may provide a means of normalizing abnormal polymorphonuclear leukocyte function in some patients with ovarian malignancies. 相似文献
69.
Karina Reiter Christoph Plutzar Dietmar Moser Philipp Semenchuk Karl-Heinz Erb Franz Essl Andreas Gattringer Helmut Haberl Fridolin Krausmann Bernd Lenzner Johannes Wessely Sarah Matej Robin Pouteau Stefan Dullinger 《Global Ecology and Biogeography》2023,32(6):855-866
Aim
Land use is the most pervasive driver of biodiversity loss. Predicting its impact on species richness (SR) is often based on indicators of habitat loss. However, the degradation of habitats, especially through land-use intensification, also affects species. Here, we evaluate whether an integrative metric of land-use intensity, the human appropriation of net primary production, is correlated with the decline of SR in used landscapes across the globe.Location
Global.Time period
Present.Major taxa studied
Birds, mammals and amphibians.Methods
Based on species range maps (spatial resolution: 20 km × 20 km) and an area-of-habitat approach, we calibrated a “species–energy model” by correlating the SR of three groups of vertebrates with net primary production and biogeographical covariables in “wilderness” areas (i.e., those where available energy is assumed to be still at pristine levels). We used this model to project the difference between pristine SR and the SR corresponding to the energy remaining in used landscapes (i.e., SR loss expected owing to human energy extraction outside wilderness areas). We validated the projected species loss by comparison with the realized and impending loss reconstructed from habitat conversion and documented by national Red Lists.Results
Species–energy models largely explained landscape-scale variation of mapped SR in wilderness areas (adjusted R2-values: 0.79–0.93). Model-based projections of SR loss were lower, on average, than reconstructed and documented ones, but the spatial patterns were correlated significantly, with stronger correlation in mammals (Pearson's r = 0.68) than in amphibians (r = 0.60) and birds (r = 0.57).Main conclusions
Our results suggest that the human appropriation of net primary production is a useful indicator of heterotrophic species loss in used landscapes, hence we recommend its inclusion in models based on species–area relationships to improve predictions of land-use-driven biodiversity loss. 相似文献70.
Sarah R. Grant Sabine Hardenack Stefan Trentmann Heinz Saedler 《Molecular genetics and genomics : MGG》1993,241(1-2):153-160
TNPA, one of the two transposition proteins encoded by the En/Spm transposable elements of Zea mays, suppresses the expression of genes that contain an appropriate cis element. Suppression can be monitored in tobacco protoplasts in a transient expression assay as follows. The plant promoter-driven expression of the Escherichia coli-glucuronidase (GUS)-encoding gene, uidA, is repressed in the presence of TNPA if the GUS gene contains a functional cis element in the untranslated RNA leader sequence. Earlier, we found that the minimal cis element is composed of two 12 by sequences in a tail-to-tail inverted orientation. Each 12 by sequence is sufficient to bind TNPA in vitro and can be thought of as a half-site in the cis element. Here, we investigated the sequence requirements of the minimal cis element. Our observations support our expectations that a functional cis element must provide a template to which two TNPA molecules can bind in the correct orientation. Sequences within the half-sites can be altered as long as the eight bases that make up the consensus binding sites are not changed. However, we found the following unexpected sequence specificities. Firstly, some changes to the consensus binding sequence can be tolerated in one half-site, as long as the other site matches the consensus. Secondly, although the region between the half-sites can vary in sequence and in length between two and four bases, a thymidine residue is not tolerated directly 5′ preceding the second half-site. Since many variants of the cis element sequence remain functional, the suppressor response element provides a flexible tool for artificially manipulating the expression of genes. 相似文献