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51.
Sequence requirements for the termination of rolling-circle replication of plasmid pT181 总被引:3,自引:0,他引:3
Most small multicopy plasmids of Gram-positive bacteria and many in Gram-negative bacteria replicate by a rolling-circle (RC) mechanism. The replication initiator proteins encoded by the RC plasmids and single-stranded bacteriophages of Escherichia coli have origin-specific nicking-closing activities that are required for the initiation and termination of RC replication. We have investigated the sequence requirements for termination of RC replication of plasmid pT181. The initiator nick site is located in the loop of a hairpin region (IRII) within the pT181 origin of replication. By mutational analysis, we have found that several nucleotides within the stem of IRII which are critical for the initiation activity are dispensable for termination of replication. We also demonstrate that nucleotides in the right arm of IRII, but not the left arm, are absolutely required for termination of RC replication. We have also identified specific nucleotides in IRII that are critical for its termination activity. The sequence of the right arm of the hairpin must be located downstream of the initiator nick site for termination, suggesting that termination requires a specific orientation of the initiator protein at the origin. 相似文献
52.
There is an active process by which sex pheromone reserves of female cabbage looper moths, Trichoplusia ni, are transported to the gland's surface during the nocturnal period of calling. We hypothesized that this mobilization was controlled by a head factor, possibly related to the pheromone biosynthesis activating neuropeptides (PBAN) that in other species stimulate pheromone synthesis. We evaluated the impact of head extracts of T. ni on pheromone emission and glandular content of pheromone. During the photophase injected head extracts stimulated an increased pheromone emission rate in females, but glandular content of pheromone was not affected. Head extracts of H. virescens, a species with known PBAN activity, and synthetic PBAN stimulated an increased pheromone emission rate in T. ni. There was some specificity of the response of female T. ni to PBAN, in that several other unrelated polypeptides did not stimulate this type of response. Previously it had been determined that brain factors do not play a role in stimulating pheromone biosynthesis in T. ni. Our results indicate that there may be additional avenues by which PBAN or related neuropeptides control pheromone emission, including transport of pheromone reserves to the surface of the sex pheromone gland. 相似文献
53.
δ-Glutamate Receptors Are Differentially Distributed at Parallel and Climbing Fiber Synapses on Purkinje Cells 总被引:1,自引:0,他引:1
Hui-Min Zhao Robert J. Wenthold Ya-Xian Wang Ronald S. Petralia 《Journal of neurochemistry》1997,68(3):1041-1052
Abstract: Neurons containing multiple excitatory inputs may sort and target glutamate receptor subtypes to subsets of synapses. A good model for testing this hypothesis is the Purkinje cell, which expresses significant levels of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate, kainate, N -methyl- d -aspartate, δ-, and metabotropic glutamate receptors. Purkinje cells receive two excitatory inputs, the parallel and climbing fibers; the combined effect of stimulation of these two inputs is to produce long-term depression of parallel fiber/Purkinje cell neurotransmission. Distribution of glutamate receptors in these two synapse populations in rat cerebella was studied using preembedding immunocytochemistry with antibodies to GluR1, GluR2/3, GluR5-7, NR1, δ1/2, and mGluR1α. Moderate/dense postsynaptic staining was most frequent in postsynaptic densities and spines of both parallel and climbing fiber synapses with mGluR1α antibody, was intermediate in frequency with GluR2/3 and GluR5-7 antibodies, and was least frequent with GluR1 and NR1 antibodies. The most striking finding was the absence of significant postsynaptic staining with δ1/2 antibody in climbing fiber synapses in adult animals, even though postsynaptic staining was prevalent in parallel fiber synapses with this antibody. In contrast to adults, moderate/dense postsynaptic immunolabeling of climbing fiber synapses with δ1/2 antibody was common in rats at 10 days postnatal. This study provides direct morphological evidence that δ-glutamate receptors are differentially targeted to synapse populations. Our results support previous suggestions that δ2 is involved in development of parallel and climbing fiber synapses and in long-term depression of parallel fiber/Purkinje synaptic responses in adults. 相似文献
54.
Physiologic and yield effects of mixtalol at various concentrations sprayed on rape at the anthesis stage were examined. Foliar sprays of 4 and 2 ppm mixtalol significantly increased the chlorophyll content of rape leaves and pods, reduced the accumulation of malondialdehyde and ethylene production, and delayed the degradation of superoxide dismutase and catalase activities of the rape plant. Mixtalol also increased root oxidizability. Meanwhile, the number of branches and pods per plant was increased, and a 10.7% and 8.2% increase of seed yield over the controls was observed with treatments of 4 and 2 ppm mixtalol, respectively. No significant effects from mixtalol were observed on the maturation of plants or on the seed oil content or the erucic acid and glucosinolate content. Total rape oil production increased with 4 and 2 ppm mixtalol significantly by 12.4% and 10.5%, respectively, over the controls.Abbreviations MTL
mixtalol
- MDA
malondialdehyde
- TBA
thiobarbituric acid
- SOD
Superoxide dismutase
- CAT
catalase
- TTC
tetrazolium 相似文献
55.
Rulin Zhao Bernadette Oreski J. William Lown 《Bioorganic & medicinal chemistry letters》1995,5(24):3063-3066
A series of new camptothecin derivatives bearing five-membered ring heterocycle containing substituents in the 10-position were synthesized and evaluated for in vitro cytotoxic activity. Camptothecin derivatives bearing a pyrrole or a thiophene ring were significantly more potent than camptothecin, however those bearing furan were less potent than camptothecin. 相似文献
56.
57.
Grantley W. Lycett Ashton J. Delauney Wenming Zhao John A. Gatehouse Ronald R. D. Croy Donald Boulter 《Plant molecular biology》1984,3(2):91-96
The sequence of two cDNA clones coding for the whole of the -subunit and most of the -subunit of legumin are presented together with a considerable amount of protein sequence data to confirm the predicted amino acid sequence. A unique feature shown by these cDNAs is the presence of three 56 base pair tandem repeats in the region encoding the C terminal of the polypeptide. The tandem repeats are also exhibited in the predicted polypeptide sequence as three 18 amino acid repeats which contain extremely high proportions of polar, mainly acidic, residues. The new sequences are compared to the previously published sequence of some shorter legumin cDNAs (Nature 295: 76–79). In the region where the sequences overlap, the previous cDNAs differ from the new ones by only a few base substitutions but most of the repeated region is not present though the sequences on either side are. The possibility that the absence of the repeats may reflect the difference between two types of legumin gene, rather than an artefact of the cloning of the cDNAs, is discussed. 相似文献
58.
59.
以走马胎(Ardisia gigantifolia)幼嫩茎段为外植体, 通过腋芽增殖的方式进行组织培养和快速繁殖研究。结果表明, 培养基MS+1.0 mg·L -1 6-BA+0.2 mg·L -1NAA和MS+0.5 mg·L -1 ZT均可用于腋芽的诱导和前期继代培养, 诱导率分别为89.3%和85.7%; 芽增殖最佳培养基为MS+0.5 mg·L -16-BA+0.1 mg·L -1ZT+0.1 mg·L -1NAA, 增殖系数为4.3倍; 根诱导最佳培养基为1/2MS+1.5 mg·L -1 IAA+1.0 mg·L -1 NAA, 生根率达92.3%, 且根系发达, 植株健壮; 生根苗在混合基质园土:泥炭:珍珠岩=3:1:1 (v/v/v )中移栽成活率为82%。该研究建立了走马胎种苗的组织培养快速繁殖技术体系, 且可应用于规模化生产。 相似文献
60.
木犀科11属19个种叶绿体基因组的一般特征和变异特征的比较分析显示, 结果表明, 该科叶绿体基因组大小为154-165 kb, 其差异主要是大单拷贝(LSC)长度的差异所致。Jasminum属3个物种的叶绿体基因组长度与其余物种有较大差异, 该属clpP基因内含子和accD基因丢失。共线性分析表明, Jasminum属3个物种多个基因出现基因重排现象, 倒位可能是重排的主要原因。Jasminum属在IRb/SSC和SSC/IRa边界的基因均与其它物种不同; 重复序列与SSR数量检测结果表明, Jasminum属与其余物种在数量及重复长度上差异较大。基于CDS数据构建的系统发育树表明, Abeliophyllum distichum和Forsythia suspensa为木犀科中较早分化的类群。 相似文献