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221.
Ana María Bravo-Angel Heinz-Albert Becker Reinhard Kunze Barbara Hohn Wen-Hui Shen 《Molecular & general genetics : MGG》1995,248(5):527-534
A reverse genetic system for studying excision of the transposable elementDs1 in maize plants has been established previously. In this system, theDs1 element, as part of the genome of maize streak virus (MSV), is introduced into maize plants via agroinfection. In the presence
of theAc element, excision ofDs1 from the MSV genome results in the appearance of viral symptoms on the maize plants. Here, we used this system to study DNA
sequences requiredin cis for excision ofDs1. TheDs1 element contains theAc transposase binding motif AAACGG in only one of its subterminal regions (defined here as the 5′ subterminal region). We showed
that mutation of these motifs abolished completely the excision capacity ofDs1. This is the first direct demonstration that the transposase binding motifs are essential for excision. Mutagenesis with
oligonucleotide insertions in the other (3′) subterminal region resulted in elements with either a reduced or an increased
excision efficiency, indicating that this subterminal region also has an important function. 相似文献
222.
Calcitonin gene-related peptide (CGRP) exerts a positive contractile response directly in rat ventricular cardiomyocytes. This response is mediated by receptors of the CGRP1-subtype. Amylin is 46% homologous with CGRP and binds to receptors selective for CGRP in a range of tissues. The ability of amylin to influence ventricular contractility has been assessed using cardiomyocytes isolated from the ventricles of adult rats. Cardiomyocytes were subjected to biphasic electrical stimulation at 0.5 Hz. CGRP produced a concentration-dependent positive contractile response which became maximal 4 min after initial stimulation. CGRP increased the contractile amplitude maximally at 1 nM and to a value which was 23.3% greater than in the absence of peptide (EC50 VALUE = 21 pM). Amylin increased the contractile amplitude maximally at 20 nM and to a value which was 17.3% greater than in the absence of peptide (EC50 VALUE = 216 pM). In the presence of amylin (20 nM), the concentration-dependence of the contractile response to CGRP was shifted to the left, so that the response became maximal when CGRP was present at 50 pM. In the presence of CGRP8–37 (100 nM), a selective antagonist at CGRP1-preferring receptors, the concentration-dependence of the contractile response to CGRP was shifted to the right (dose RATIO = 54). Similarly, in the presence of CGRP8–37 (100 nM), the contractile response to amylin was inhibited significantly (P ≤ 0.01). Amylin8–37 (100 nM) did not inhibit the concentration-dependence of the contractile responses to CGRP and amylin significantly (dose RATIOS = 4.2 and 2.4, respectively). In conclusion, these data indicate that amylin exerts a contractile response directly in rat ventricular cardiomyocytes via CGRP1-preferring receptors. This effect could assume greater significance in non-insulin-dependent diabetes mellitus and in hypertensive states, in which the concentration of amylin is elevated in plasma. 相似文献
223.
Barbara C. Boyer 《Hydrobiologia》1995,305(1-3):217-222
In spiralian embryos determination of the axes of bilateral symmetry is associated with D quadrant specification. This can occur late through equal cleavage and cell interactions (conditional specification) or by the four-cell stage through unequal cleavage and cytoplasmic localization (autonomous specification). Freeman & Lundelius (1992) suggest that in spiralian coelomates the former method is ancestral and the latter derived, with evolutionary pressure to shorten metamorphosis resulting in early D quadrant determination through unequal cleavage and appearance of adult features in the larvae. Because of the key phylogenetic position of the turbellarian platyhelminthes, understanding the method of axis specification in this group is important in evaluating the hypothesis. Polyclad development, with equal quartet spiral cleavage, is believed to represent the most primitive condition among living turbellarians and has been examined experimentally in Hoploplana inquilina. Blastomere deletions at the two and four-cell stage produce larvae that are abnormal in morphology and symmetry, indicating that early development is not regulative, and also establish that the embryo does not have an invariant cell lineage. Deletions of micromeres and macromeres at the eight-cell stage indicate that cell interactions are involved in dorso-ventral axis determination, with cross-furrow macromeres playing a more significant role than non-cross-furrow cells. The results support the idea that conditional specification is the primitive developmental mode that characterized the common ancestor of the turbellarians and spiralian coelomates. Evolutionary trends in development in polyclads and other turbellarian orders are discussed. 相似文献
224.
New evidence for the systematic significance of acylated spermidines and flavonoids in pollen of Higher Hamamelidae 总被引:1,自引:0,他引:1
Barbara Meurer-Grimes 《Brittonia》1995,47(2):130-142
New distributional recores of hydroxycinnamoyl spermidines (HCS), including novel trisubstituted HCSs and flavonol glycosides,
in pollen of Higher Hamamelidae are presented. The 51 taxa analyzed by HPLC and TLC included members of the families Fagaceae
(Castanoideae, Fagoideae, Quercoideae), Betulaceae, Juglandaceae, Myricaceae, Hamamelidaceae, Rosaceae, and Buxaceae (Simmondsia). The results support generic concepts in the Higher Hamamelidae derived from morphological and chloroplast DNA data and
support a close evolutionary relationship between the Higher Hamamelidae and the Rosidae. 相似文献
225.
David A. Flemer Roman S. Stanley Barbara F. Ruth Charles M. Bundrick Paul H. Moody James C. Moore 《Hydrobiologia》1995,308(2):85-101
Two six-week laboratory experiments were conducted to evaluate effects of pesticides and microcosm size on benthic estuarine
macroinvertebrate recolonization. Sediments fortified with the pesticides (fenvalerate: controls, 5 (low) and 50 μg g−1 wet sediment (high); endosulfan: controls, 1 (low) and 10 μg g−1 wet sediment (high)) were fine-grained, organically rich (approximately 3.5% organic carbon and 22% dry weight) material.
Relative dominance of the four most abundant taxa in both experiments was consistent among treatments with few exceptions.
The amphipod,Corophium acherusicum, dominated abundance in both experiments.
In the fenvalerate experiment, large trays (400 cm2) contained significantly (p<0.05) more total number of taxa (TNT) than small microcosms (144 cm2) but tray size was not significantly related to total number of organisms (TNO). When size was adjusted to a common unit
area, small trays contained significantly more TNO than large containers. Adjusted abundance of small trays was 2.5 times
that of large containers; a ratio close to that of microcosm sizes (i.e., 2.8). This result suggests that larval supply may have been inadequate to ‘aturate’ the available sediment in large containers.
Fenvalerate significantly reduced abundance in the high treatment compared to both controls and low treatment but low treatment
was not significantly different from controls. The amphipod,Corophium acherusicum, accounted for most of the decrease in abundance in response to fenvalerate. The holothruroid,Leptosynpta sp. and the polychaete,Mediomastus ambiseta, increased in abundance significantly with increased concentration of fenvalerate.
Combined effects of actual microcosm size and concentration of endosulfan were not significant for TNO or TNT. As in the fenvalerate
experiment, adjusted abundance of small microcosms was 2.6 times that of large trays which approximated the ratio of unit
area between microcosm sizes. Abundance of a few taxa responded significantly to adjusted and unadjusted unit area. Abundance
of the tunicate,Molgula manhattensis, increased significantly with increased concentration of endosulfan. Abundance was affected by sample location (e.g., interiorvs exterior cores) within microcosms. Abundance adjusted to unit area resulted in significantly greater TNO in externalvs internal cores. This has importance for sequential sub-sampling of microcosms to determine temporal dynamics.
Statistically significant effects were measured in benthic community structure associated with microcosm size; however, the
magnitude was relatively small. There appears to be no major biological reason to select one microcosm size over the other
for screening for contaminant effects. Where feasible, the small trays provide savings in sample preparation and analysis,
allow more replicates where laboratory space is limiting and generate less chemical waste. These benefits may be off-set by
less ‘artifacts’ associated with edge effects of larger microcosms and the need for a larger mass of sediment to accommodate
additional analytical requirements (e.g., thin vertical surficial samples to refine contaminant exposure at the sediment/water
interface). 相似文献
226.
Alexander A. Kortt Robin E. Guthrie Mark G. Hinds Barbara E. Power Neva Ivancic J. Bruce Caldwell L. Clem Gruen Raymond S. Norton Peter J. Hudson 《Journal of Protein Chemistry》1995,14(3):167-178
The VH domain of anti-influenza neuraminidase antibody NC41, with and without a C-terminal hydrophilic marker peptide (FLAGTM), has been expressed in high yield (15–27 mg/L) inEscherichia coli. Both forms were secreted into the periplasm where they formed insoluble aggregates which were solubilized quantitatively with 2 M guanidine hydrochloride and purified to homogeneity by ion-exchange chromatography. The VH-FLAG was composed of three isoforms (pI values of 4.6, 4.9, and 5.3) and the VH molecule was composed of two isoforms with pI values of 5.1 and 6.7; the difference between the VH isoforms was shown to be due to cyclization of the N-terminal glutamine residue in the pI 5.1 isoform. At 20°C and concentrations of 5–10mg/ml the VH domain dimerized in solution and then partly precipitated, resulting in the broadening of resonances in its1H NMR spectrum. Reagents such as CHAPS,n-octylglucoside, and ethylene glycol, which presumably mask the exposed hydrophobic interface of the VH molecule, prevented dimerization of the VH and permitted good-quality NMR spectra on isotope-labeled protein to be obtained. 相似文献
227.
228.
In this study we describe the contribution of matrilineal and patrilineal effects on the adiposity, body weight, and on the
weights of individual fat pads in F2 male mice derived from an SWR/J × AKR/J cross. AKR/J mice become obese after 12 weeks on a high-fat diet, whereas SWR/J mice
remain relatively lean. Here we report that mice with AKR maternal and AKR paternal grandmothers have significantly larger
epidydimal and retroperitoneal fat pads than those with SWR maternal and paternal grandmothers. However, grandparental strain
had no effect on the overall adiposity (AI) or the weights of the inguinal, subcutaneous or mesenteric fat pads. The strain
of the paternal grandparents had a small but significant effect on body weight. These effects can be attributed to in utero
effects, imprinting effects, cytoplasmic and/or Y chromosome transmission of factors controlling body fat. We also describe
the presence of a quantitative trait locus (QTL) on Chromosome X, close to DXMit174, which is linked to adiposity, body weight, and to the weights of the individual fat depots. However, this QTL is not responsible
for the grandparental strain effects described above.
Received: 3 March 1997 / Accepted: 5 May 1997 相似文献
229.
Søren Bak Rachel Alice Kahn Carl Erik Olsen Barbara Ann Halkier 《The Plant journal : for cell and molecular biology》1997,11(2):191-201
Obtusifoliol 14β-demethylase from Sorghum bicolor (L.) Moench has been cloned using a gene-specific probe generated using PCR primers designed from an internal 14 amino acid sequence. The sequence identifies sorghum obtusifoliol 14α-demethylase as a cytochrome P450 and it is assigned to the CYP51 family together with the sterol 14α-demethylases from fungi and mammals. The presence of highly conserved regions in the amino acid sequences, analogous substrates and the same metabolic role demonstrate that the sterol 14α-demethylases are orthologous enzymes. The sterol 14α-demethylases catalyse an essential step in sterol biosynthesis as evidenced by the absence of a 14α-methyl group in all known functional sterols. A functional sorghum obtusifoliol 14α-demethylase was expressed at high levels in Escherichia coli and purified using an efficient method based on temperature-induced Triton X-114 phase partitioning. The recombinant purified enzyme produced a type I spectrum with obtusifoliol as substrate. Reconstitution of purified recombinant enzyme with sorghum NADPH—cytochrome P450 reductase in dilaurylphosphatidylcholine micelles confirms that obtusifoliol 14α-demethylase catalyses the 14α-demethylation of obtusifoliol to 4α-methyl-5α-ergosta-8,14,24(28)-trien-3β-ol as evidenced by GC—MS. The isolation of a cDNA clone encoding the plant sterol 14α-demethylase, combined with the previously isolated cDNA clones for fungal and mammalian sterol 14α-demethylases, provides an important tool in the rational design of specific inhibitors towards the individual sterol 14α-demethylases. 相似文献
230.
Barbara Thöni 《Journal of Ornithology》1997,138(3):315-324
Zusammenfassung Im Frühjahr 1995 (Febr.–Mai) wurden auf der Schwäbischen Alb 7 Kolkrabenpaare beobachtet. Ziel der Untersuchung war es den Aufwand der Altvögel für die Jungenaufzucht zu erfassen. Der Aufwand wurde über die Aktivität der Altvögel am Nest abgeschätzt und bezüglich der Jungenzahl und des Wetters ausgewertet. Paare, die mehrere Junge hatten, sparten beim Hudern Kosten ein, da sie ihre Jungen bis zu einem geringeren Alter hudern mußten und weniger stark von der Temperatur abhängig waren. Bei den Fütterungen verringerte sich die Fütterfrequenz pro Jungvogel mit zunehmender Jungenzahl, die absolute Anzahl an Fütterungen nahm jedoch zu. Der Aufwand für die Nesthygiene war unabhängig von der Jungenzahl. Selbst bei mehreren Jungen blieb Zeit für Komfortverhalten. Jungenaufzucht war also effektiver, wenn mehrere Jungen gleichzeitig aufgezogen wurden.
Parental expenditure for rearing nestlings by ravensCorvus corax
In spring 1995 (Feb.–May) I observed seven pairs of Raven in southern Germany on the Schwäbischen Alb. The aim was to record parental expenditure for rearing nestlings. Expenditure was assessed by recording the activities of the adults at their nest (mainly brooding and feeding the offspring) and was analysed with respect to the number of nestlings per brood and with respect to the weather. Pairs with more than one nestling saved effort by stopping brooding their offspring at a lower nestling age. Also brooding was less dependent on the ambient temperature for pairs with more than one nestling than for pairs with only one nestling. The feeding frequency per nestling has been lower, if there were more nestlings to feed. The total frequency of feeding increased with increasing number of nestlings per brood. The effort for the hygiene of the nest was independent upon the number of offspring per nest. Nevertheless, pairs with more than one nestling spent time for comfort behaviour. Thus, it was more effective to reare more than one nestling at a time.相似文献