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991.
Balhorn R 《Genome biology》2007,8(9):227
The protamines are a diverse family of small arginine-rich proteins that are synthesized in the late-stage spermatids of many
animals and plants and bind to DNA, condensing the spermatid genome into a genetically inactive state. Vertebrates have from
one to 15 protamine genes per haploid genome, which are clustered together on the same chromosome. Comparison of protamine
gene and amino-acid sequences suggests that the family evolved from specialized histones through protamine-like proteins to
the true protamines. Structural elements present in all true protamines are a series of arginine-rich DNA-anchoring domains
(often containing a mixture of arginine and lysine residues in non-mammalian protamines) and multiple phosphorylation sites.
The two protamines found in mammals, P1 and P2, are the most widely studied. P1 packages sperm DNA in all mammals, whereas
protamine P2 is present only in the sperm of primates, many rodents and a subset of other placental mammals. P2, but not P1,
is synthesized as a precursor that undergoes proteolytic processing after binding to DNA and also binds a zinc atom, the function
of which is not known. P1 and P2 are phosphorylated soon after their synthesis, but after binding to DNA most of the phosphate
groups are removed and cysteine residues are oxidized, forming disulfide bridges that link the protamines together. Both P1
and P2 have been shown to be required for normal sperm function in primates and many rodents. 相似文献
992.
Brüser T 《Applied microbiology and biotechnology》2007,76(1):35-45
The biotechnological production of recombinant proteins is challenged by processes that decrease the yield, such as protease
action, aggregation, or misfolding. Today, the variation of strains and vector systems or the modulation of inducible promoter
activities is commonly used to optimize expression systems. Alternatively, aggregation to inclusion bodies may be a desired
starting point for protein isolation and refolding. The discovery of the twin-arginine translocation (Tat) system for folded
proteins now opens new perspectives because in most cases, the Tat machinery does not allow the passage of unfolded proteins.
This feature of the Tat system can be exploited for biotechnological purposes, as expression systems may be developed that
ensure a virtually complete folding of a recombinant protein before purification. This review focuses on the characteristics
that make recombinant Tat systems attractive for biotechnology and discusses problems and possible solutions for an efficient
translocation of folded proteins. 相似文献
993.
994.
A complex formation between hemin and a congruous oligonucleotide not only greatly enhances the former’s peroxidative activity
but also results in a biocatalyst (DNAzyme) with a novel specificity. Herein substrate, regio-, enantiomeric, and diastereomeric
selectivities of heme, the DNAzyme, and the enzyme horseradish peroxidase are comparatively examined. 相似文献
995.
Cedar M. Chittenden Kevin G. Butterworth K. Fiona Cubitt Melinda C. Jacobs Adrian Ladouceur David W. Welch R. Scott McKinley 《Environmental Biology of Fishes》2009,84(1):129-140
Many coho salmon stocks (Oncorhynchus kisutch) have been in decline during the past three decades. Canada’s most endangered salmon stock, the Thompson River coho salmon,
is being studied extensively as managers attempt to reverse these population declines. Investigators are using acoustic telemetry
to track the migratory behaviour and survival of the Thompson River (and other) coho salmon stocks. Coho salmon pre-smolts
are relatively small compared with salmonid species that are typically studied using acoustic telemetry; therefore the identification
of the appropriate sizes of fish and tags to use is critical. This study tested the effects of surgically implanting the three
smallest sizes of acoustic tags currently available on the growth, survival, tag retention, swimming performance and physical
condition of coho salmon pre-smolts for 300 days post-surgery. Maximum tag size to body size ratios ranged from 15–17% by
fork length and 7–8% by mass for the three tag sizes (11 cm fork length for a 6 × 19 mm tag, 12.5 cm for a 7 × 19 mm tag,
and 14 cm for a 9 × 21 mm tag). Based on our results, it is unlikely that coho salmon pre-smolts implanted with acoustic transmitters
following these size guidelines would have poor survival in studies of freshwater migratory behaviour as a result of the surgery
or the tag. 相似文献
996.
Secondary succession is an increasing phenomenon due to global changes in agriculture policies and practices. The empirical
findings are biased towards the temperate zone. Abandonment of agriculture fields is less frequent in the subtropical and
tropical zones where agriculture areas are, in general, expanding. But there are exceptions; a rapid rate of abandonment of
agricultural fields have taken place in the arid trans-Himalayan region, due to today’s globalization of economy. We analysed agriculture fields that were abandoned between 1950
and 2003 in a large u-valley in central Nepal (3400 m a.s.l.). The potential forest vegetation is dominated by Pinus wallichina and shrubs of junipers and cotoneaster species. We tested the intermediate richness hypothesis in relation to vegetation
cover, soil development and whether old-field succession is convergent or divergent with species data from 242 1 m2 plots in 5 age-classes. The main species compositional turnover expressed by Detrended Correspondence Analyses (DCA) correlated,
as expected, with time after abandonment. Fields that were abandoned a long time ago are closer to forest at the periphery
of the agricultural landscape. Moisture of the soil significantly increased with age of abandonment, but total vegetation
cover and pH were negatively related to age. Beta diversity expressed in DCA SD-units showed an increasing trend with age
of abandonment, supporting the divergence pattern in old-field succession. The reason why the succession is not converging
may be due to browsing by domestic animals that prevent a closed canopy of pines and juniper to develop. There was a significant
hump-shaped pattern in species richness along the temporal gradient, which agrees with the intermediate species-richness hypothesis.
There was a rapid increase in species richness in plots close to the villages that were used for haymaking which increased
the seed input significantly. 相似文献
997.
Michael Denker Alexa Riehle Markus Diesmann Sonja Grün 《Journal of computational neuroscience》2010,29(3):599-613
The hypothesis that cortical networks employ the coordinated activity of groups of neurons, termed assemblies, to process
information is debated. Results from multiple single-unit recordings are not conclusive because of the dramatic undersampling
of the system. However, the local field potential (LFP) is a mesoscopic signal reflecting synchronized network activity. This
raises the question whether the LFP can be employed to overcome the problem of undersampling. In a recent study in the motor
cortex of the awake behaving monkey based on the locking of coincidences to the LFP we determined a lower bound for the fraction
of spike coincidences originating from assembly activation. This quantity together with the locking of single spikes leads
to a lower bound for the fraction of spikes originating from any assembly activity. Here we derive a statistical method to
estimate the fraction of spike synchrony caused by assemblies—not its lower bound—from the spike data alone. A joint spike
and LFP surrogate data model demonstrates consistency of results and the sensitivity of the method. Combining spike and LFP
signals, we obtain an estimate of the fraction of spikes resulting from assemblies in the experimental data. 相似文献
998.
999.
A strain of canine parvovirus (CPV) was isolated from feces of an ill puppy in an animal hospital in Wuhan, China. It was designated as CPV/WH02/06. This isolate was identified as serotype CPV-2a by the hemagglutination test, CPV Ag detection strip, electron microscopy, and PCR. The vp2 gene was cloned and sequenced and assigned GenBank accession number EU377537. A 1242 bp segment of the 5' region of the vp2 gene was cloned and inserted into the binary vector pBI121 and used for Agrobacterium-mediated tobacco transformation. Transgenic tobacco plants were selected on MS medium supplemented with 100 μg/mL kanamycin and 100 μg/mL timentin. Integration of the vp2 gene into the tobacco genome was confirmed by PCR using T1 progeny plants, and the expression of the VP2 protein was confirmed by Western blotting. 相似文献
1000.