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1.
Isolation of viral coat protein mutants with altered assembly and aggregation properties 总被引:1,自引:0,他引:1
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A method was developed to screen bacteria for synthesis of mutant proteins with altered assembly and solubility properties using bacteriophage MS2 coat protein as a model self-associating protein. Colonies expressing coat protein from a plasmid were covered with an agarose overlay under conditions that caused the lysis of some of the cells in each colony. The proteins thus liberated diffused through the overlay at rates depending on their molecular sizes. After transfer of the proteins to a nitrocellulose membrane, probing with coat protein-specific antiserum revealed spots whose sizes and intensities were related to the aggregation state of coat protein. The method was employed in the isolation of assembly defective mutants and to find soluble variants of an aggregation-prone coat protein mutant. 相似文献
2.
Semiparametric Regression in Size-Biased Sampling 总被引:1,自引:0,他引:1
Ying Qing Chen 《Biometrics》2010,66(1):149-158
Summary . Size-biased sampling arises when a positive-valued outcome variable is sampled with selection probability proportional to its size. In this article, we propose a semiparametric linear regression model to analyze size-biased outcomes. In our proposed model, the regression parameters of covariates are of major interest, while the distribution of random errors is unspecified. Under the proposed model, we discover that regression parameters are invariant regardless of size-biased sampling. Following this invariance property, we develop a simple estimation procedure for inferences. Our proposed methods are evaluated in simulation studies and applied to two real data analyses. 相似文献
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Lina Long Douglas R. McCabe M. Eileen Dolan 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1999,731(2):128
A highly sensitive and selective method for determining 8-oxoguanine in plasma and urine was developed by high-performance liquid chromatography with electrochemical detection. The compound was separated by gradient elution on a C18 reversed-phase column with a mobile phase of acetonitrile and 0.1 M sodium acetate, pH 5.2. 8-Hydroxy-2′-deoxyguanosine was used as internal standard. 8-Oxoguanine was detected electrochemically by setting the potential to +300 mV vs. Pd reference. The sensitivity of the assay was 22 ng/ml with a signal-to-noise ratio of 7:1. The within-day relative standard deviations for 8-oxoguanine quality control samples with concentrations of 3340, 1340 and 84 ng/ml were 3.6, 4.3 and 5.7% for plasma, and 4.1, 4.6 and 6.2% for urine, respectively. The day-to-day relative standard deviations for the same samples were 3.8, 6.8 and 7.1% for plasma, and 3.9, 7.0 and 7.9% for urine, respectively. The method is designed to study the pharmacokinetics and metabolic fate of O6-benzylguanine in a phase I clinical trial. Previously, O6-benzyl-8-oxoguanine was identified as the primary metabolite of O6-benzylguanine in humans. We now demonstrate that 8-oxoguanine is a further metabolite of O6-benzylguanine. 相似文献
6.
Lina L. E. Massone 《Biological cybernetics》1994,71(4):293-305
This paper presents a neural-network-based system that can generate and control movements of the eyes. It was inspired by a number of experimental observations on the saccadic and gaze systems of monkeys and cats. Because of the generality of the approach undertaken, the system can be regarded as a demonstration of how parallel distributed processing principles, namely learning and attractor dynamics, can be integrated with experimental findings, as well as a biologically inspired controller for a dexterous robotic orientation device. The system is composed of three parts: a dynamic motor map, a push-pull circuitry, and a plant. The dynamics of the motor map is generated by a multi-layer network that was trained to compute a bidimensional temporal-spatial transformation. Simulation results indicate (1) that the system is able to reproduce some of the properties observed in the biological system at the neural and movement levels and (2) that the dynamics of the motor map remains stereotyped even when the motor map is subject to abnormal stimulation patterns. The latter result emphasizes the role of the topographic projection that connects the motor map to the push-pull circuitry in determining the features of the resulting movements. 相似文献
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Intermittent tongue, lip and cheek forces influence precise tooth position, so we here examine the possibility that tissue remodelling driven by functional bite-force-induced jaw-strain accounts for tooth eruption. Notably, although a separate true ‘eruptive force’ is widely assumed, there is little direct evidence for such a force. We constructed a three dimensional finite element model from axial computerized tomography of an 8 year old child mandible containing 12 erupted and 8 unerupted teeth. Tissues modelled included: cortical bone, cancellous bone, soft tissue dental follicle, periodontal ligament, enamel, dentine, pulp and articular cartilage. Strain and hydrostatic stress during incisive and unilateral molar bite force were modelled, with force applied via medial and lateral pterygoid, temporalis, masseter and digastric muscles. Strain was maximal in the soft tissue follicle as opposed to surrounding bone, consistent with follicle as an effective mechanosensor. Initial numerical analysis of dental follicle soft tissue overlying crowns and beneath the roots of unerupted teeth was of volume and hydrostatic stress. To numerically evaluate biological significance of differing hydrostatic stress levels normalized for variable finite element volume, ‘biological response units’ in Nmm were defined and calculated by multiplication of hydrostatic stress and volume for each finite element. Graphical representations revealed similar overall responses for individual teeth regardless if incisive or right molar bite force was studied. There was general compression in the soft tissues over crowns of most unerupted teeth, and general tension in the soft tissues beneath roots. Not conforming to this pattern were the unerupted second molars, which do not erupt at this developmental stage. Data support a new hypothesis for tooth eruption, in which the follicular soft tissues detect bite-force-induced bone-strain, and direct bone remodelling at the inner surface of the surrounding bony crypt, with the effect of enabling tooth eruption into the mouth. 相似文献
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Wei de Zhang Fan Qing Li Xiao Yun Zhang Ying Chen 《Biological trace element research》1988,17(1):81-90
The growth of the protozoanBlepherisma is stimulated by Lanthanum (La) at concentrations as low as 0.32 ppm. In mice Yttrium (Y) and Ytterbium (Yb) are absorbed,
accumulated, and metabolized. Both rare earth elements (RE) exhibit a high affinity for teeth and bones, accumulation occurs
and metabolism is slow. In the livers of RE-exposed mice, concentrations are variable. The liver is apparently capable of
absorbing and discharging RE in a manner depending on metabolic activity. The main route of discharge for ingested REs is
the alimentary canal. Exposure of pregnant mice to RE leads to rapid placental transfer of RE; 14.1% of the total amount of
RE administered was detected in newborn mice. Young, developing organisms appear to be especially susceptible to RE accumulation. 相似文献
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