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排序方式: 共有195条查询结果,搜索用时 434 毫秒
161.
REINDERS J. E. A.; AS H. VAN; SCHAAFSMA T. J.; SHERIFF D. W. 《Journal of experimental botany》1988,39(9):1211-1220
Nuclear magnetic resonance (NMR) was used to investigate theeffects of changes in root temperature, of changes in the areaof root in contact with culture solution and of day/night rhythmon the water balance of a cucumber and a gherkin plant. Resultsare discussed in terms of water potential, flow rate and resistanceusing a previously presented model of water balance. As longas water uptake alone is varied, flow rate and water content(or potential) will change in the same direction. In contrast,from that model it is predicted that changes in transpirationwill affect flow rate and water content in opposite ways. Anexperimental verification of this prediction was given in theprevious paper. Results obtained by the NMR method are comparedto those determined using a dendrometer. The results demonstratethat the NMR method is a valuable tool to study plant waterbalance and that it can serve as a technique for discriminatingbetween changes in plant water balance that are due to changesin water uptake by roots and those due to changes in transpiration. Key words: Water balance model, Cucumis satious L., flow, water content, NMR, water balance measurement 相似文献
162.
A new method for the enrichment of cultures of Serratia marcescens for auxotrophic mutants has been developed. The method is based on the formation of filaments by growing cells in minimal medium M70 containing azthreonam. Auxotrophic mutants unable to grow in M70 do not form filaments. Mutants are collected from the culture by filtration. 相似文献
163.
Dimerization of simian virus 40 T-antigen hexamers activates T-antigen DNA helicase activity. 总被引:5,自引:5,他引:0 下载免费PDF全文
Chromosomal DNA replication in higher eukaryotes takes place in DNA synthesis factories containing numerous replication forks. We explored the role of replication fork aggregation in vitro, using as a model the simian virus 40 (SV40) large tumor antigen (T antigen), essential for its DNA helicase and origin-binding activities. Previous studies have shown that T antigen binds model DNA replication forks primarily as a hexamer (TAgH) and to a lesser extent as a double hexamer (TAgDH). We find that DNA unwinding in the presence of ATP or other nucleotides strongly correlates with the formation of TAgDH-DNA fork complexes. TAgH- and TAgDH-fork complexes were isolated, and the TAgDH-bound fork was denatured at a 15-fold-higher rate during the initial times of unwinding. TAgDH bound preferentially to a DNA substrate containing a 50-nucleotide bubble, indicating the bridging of each single-stranded DNA/duplex DNA junction, and this DNA molecule was also unwound at a high rate. Both the TAgH- and TAgDH-fork complexes were relatively stable, with the half-life of the TAgDH-fork complex greater than 40 min. Our data therefore indicate that the linking of two viral replication forks serves to activate DNA replication. 相似文献
164.
Evolutionary history of the COII/tRNALys intergenic 9 base pair deletion in human mitochondrial DNAs from the Pacific 总被引:14,自引:2,他引:12
Redd AJ; Takezaki N; Sherry ST; McGarvey ST; Sofro AS; Stoneking M 《Molecular biology and evolution》1995,12(4):604-615
Length changes in human mitochondrial DNA (mtDNA) are potentially useful
markers for inferring the evolutionary history of populations. One such
length change is a nine base pair (9-bp) deletion that is located in the
intergenic region between the COII gene and the Lysine tRNA gene
(COII/tRNALys intergenic region). This deletion has been used as a genetic
marker to trace descent from peoples of East Asian origin. A geographic
cline of the deletion frequency across modern Pacific Islander populations
suggests that the deletion may be useful for tracing prehistoric Polynesian
origins and affinities. Mitochondrial DNA sequence variation within two
variable segments of the control region (CR) permits a number of inferences
regarding the evolutionary history of the 9-bp deletion that cannot be
determined from frequency data alone. We obtained CR sequences from 74
mtDNAs with the 9-bp deletion from Indonesia, coastal Papua New Guinea
(PNG), and American Samoa. Phylogenetic and pairwise distribution analysis
of these CR sequences pooled with previously published CR sequences reveals
that the deletion arose independently in Africa and Asia and suggests
possible multiple origins of the deletion in Asia. A clinal increase of the
frequency of the 9-bp deletion across the three Pacific populations is
associated with a decrease in CR sequence diversity, consistent with
founder events. Furthermore, analysis of pairwise difference distributions
indicates an expansion time of proto-Polynesians that began 5,500 yr ago
from Southeast Asia. These results are consistent with the express train
model of Polynesian origins.
相似文献
165.
166.
A. terreus isolates isolated from some bakery products, corn and rice were found to be able to produce territrems. 90% of theA. terreus isolated from bakery products were able to produce territrem A, with a mean of 0.09 ppm, while 80% ofA. terreus isolates produce territrem B with a mean of 0.24 ppm. On the other hand 31.8% of the isolates ofA. terreus from corn were able to produce territrem A with a mean of 0.44 ppm. ConcerningA. terreus isolates from rice, 66.7% were found to produce territrem A, with a mean of 5.28 ppm, and 77.8% of the isolates produced
territrem B with a mean of 1.79 ppm. 相似文献
167.
Rekowski Piotr Borowiec Agnieszka Drużyńska Joanna Kusiak Elżbieta 《International journal of peptide research and therapeutics》1998,5(5-6):417-420
Summary The solid-phase synthesis andin vitro assays on the glucose-induced insulin secretion from rat pancreatic islets of Langerhans with six new chimeric peptides were
performed. All the peptides were built up of the N-terminal galanin (GAL) fragment or its analogues, linked to the C-terminal
portion of substance P (SP) analogues or scyliorhinin I (SCY-I) analogues. Two strong antagonists of the inhibitory effect
of galanin on the glucose-induced insulin release were found: [cycloleucine4]GAL(1–13)-SP(5–11)-amide and GAL(1–13)-[L-norleucine10]SCY-I(3–10)-amide. 相似文献
168.
169.
Strand and face: the topography of interactions between the SV40 origin of replication and T-antigen during the initiation of replication. 总被引:13,自引:2,他引:11 下载免费PDF全文
The mechanism by which a replicator (origin of replication) becomes denatured during the initiation of replication is not understood for any prokaryotic or eukaryotic system. To address this question, we chemically probed the molecular contacts on the SV40 origin of replication (ori) that are used by the SV40 large T-antigen and a single-stranded DNA-binding protein (SSB) during ori denaturation. Prior to the actual denaturation step, the T-antigen double hexamer bound ori utilizing sugar-phosphate contacts that were located on opposite strands in each flanking domain of ori. Each set of flanking phosphate contacts were also located on approximately opposite faces of the ori duplex. While the phosphate contacts had a 2-fold symmetry with respect to the ori center, T-antigen contacts with nucleotide bases were polar with critical interactions detected in only one of the two flanking domains. During origin denaturation catalyzed by T-antigen and a SSB, numerous new contacts to flanking phosphates were observed on the strand not initially bound by T-antigen, suggesting movement of each T-antigen hexamer outward from ori. These data suggest that T-antigen initially binds ori in a manner that facilitates transfer of each T-antigen hexamer to opposite strands during the initiation of SV40 replication. 相似文献