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161.
Human β-defensin (HBD)-2 is a small cationic peptide with a broad range of antimicrobial activity. In this study, multiple
copies of the hBD2 gene were linked in tandem, and a number of different Escherichia coli expression vectors were evaluated, including pQE-30, pBV220, pET-28a(+), and pGEX-4T-2. No expression of multiple joined
genes was detectable in the pQE-30 expression system, whereas in pBV220 with one or two joined hBD2 genes and in pET-28a(+)
with one, two, or four copies, target proteins were expressed at a low level. Only when pGEX-4T-2 was applied as expression
plasmid with one or two joined hBD2 genes were target proteins expressed in high level, and the expressed fusion proteins
account for 26 and 16% of the total insoluble proteins, respectively. In the pGEX-4T-2 and pET-28a(+) expression systems,
the effects of multiple joined genes on the growth of host strains and plasmid stability were examined. Host cells containing
plasmid carrying fewer copies of hBD2 genes were faster in cell growth. Plasmid stability decreased with an increase in multiple
joined genes, which was especially noticeable in the pET-28a(+) system. Furthermore, the presence of glucose in culture medium
brought about a positive effect on plasmid stability when using pET28-nhBD2 as expression vectors. 相似文献
162.
Pt(1 1 0) is one of the most closely investigated metal surface structures because it displays a variety of “missing-row” reconstructions, which are only marginally stable. The ground state is usually found to have 1 × 2 translational symmetry, but a 1 × 3 form has also been seen. Between 1 × 2 and 1 × 3, a series of disordered structures has been recorded, which shows a slight preference for 1 × 5 periodicity. Under the preparation conditions used in this study, a stable 1 × 5 structure was found for Pt(1 1 0). Investigation by surface X-ray diffraction has led to a complete three-dimensional structure, which closely resembles an alternation of 1 × 2 and 1 × 3 unit cells. Pt(1 1 0) shows an interesting example of two “homometric” structures that are indistinguishable by diffraction, but are distinguishable by virtue of their subsurface relaxation pattern. 相似文献
163.
基因组学进行肿瘤分型中的基因筛选方法进行探讨,根据相关分析和95%参考值范围的概念确定筛选基因的方法,该方法利用了所有基因的信息,计算简便,在对白血病患者分型时取得了很好的效果. 相似文献
164.
尿酸盐转运子基因是近年全基因组扫描锁定的高尿酸血症和痛风易感基因, 如SLC22A12、SLC2A9、ABCG2基因等, 其编码肾尿酸盐转运系统相关蛋白质, 参与肾脏对尿酸的重吸收和分泌. 目前锁定的尿酸盐转运子基因可解释约7%的血尿酸水平变异, 有影响力的位点期待被发现. 已有研究将这些易感基因应用到药物基因组学及孟德尔随机化研究领域, 是未来新的发展方向. 相似文献
165.
Zhiwei Zhang Howard E. Rockette 《Annals of the Institute of Statistical Mathematics》2006,58(4):687-706
We consider parameter estimation in parametric regression models with covariates missing at random. This problem admits a
semiparametric maximum likelihood approach which requires no parametric specification of the selection mechanism or the covariate
distribution. The semiparametric maximum likelihood estimator (MLE) has been found to be consistent. We show here, for some
specific models, that the semiparametric MLE converges weakly to a zero-mean Gaussian process in a suitable space. The regression
parameter estimate, in particular, achieves the semiparametric information bound, which can be consistently estimated by perturbing
the profile log-likelihood. Furthermore, the profile likelihood ratio statistic is asymptotically chi-squared. The techniques
used here extend to other models. 相似文献
166.
用地戈辛标记的原位杂交技术研究黄鳝二价体上rRNA基因的多态性.共检测到:数目和位置多态;杂交信号形态多态;rRNA基因的联合现象;7号二价体上可移动的rRNA基因位点;rRNA基因的串联重复;rRNA基因杂交信号周围的微信号密集等6种多态现象.还对本研究结果进行了详细地讨论. 相似文献
167.
Fan Li Michela Baccini Fabrizia Mealli Elizabeth R. Zell Constantine E. Frangakis Donald B. Rubin 《Journal of computational and graphical statistics》2013,22(3):877-892
Multiple imputation (MI) has become a standard statistical technique for dealing with missing values. The CDC Anthrax Vaccine Research Program (AVRP) dataset created new challenges for MI due to the large number of variables of different types and the limited sample size. A common method for imputing missing data in such complex studies is to specify, for each of J variables with missing values, a univariate conditional distribution given all other variables, and then to draw imputations by iterating over the J conditional distributions. Such fully conditional imputation strategies have the theoretical drawback that the conditional distributions may be incompatible. When the missingness pattern is monotone, a theoretically valid approach is to specify, for each variable with missing values, a conditional distribution given the variables with fewer or the same number of missing values and sequentially draw from these distributions. In this article, we propose the “multiple imputation by ordered monotone blocks” approach, which combines these two basic approaches by decomposing any missingness pattern into a collection of smaller “constructed” monotone missingness patterns, and iterating. We apply this strategy to impute the missing data in the AVRP interim data. Supplemental materials, including all source code and a synthetic example dataset, are available online. 相似文献
168.
Michael Friendly 《Journal of computational and graphical statistics》2013,22(1):158-166
Abstract This note extends the construction of the design matrix used for estimating cell probabilities with ignorable missing data described by Lipsitz, Parzen, and Molenberghs. A reformulation for the general case of an n-way table is described and implemented in a SAS macro program. The macro constructs this design matrix and offset variable, estimates the cell probabilities, and returns a table with the estimates, their standard errors, and fitted cell frequencies. 相似文献
169.
《Journal of computational and graphical statistics》2013,22(2):332-353
Spatial scan density (SSD) estimation via mixture models is an important problem in the field of spatial statistical analysis and has wide applications in image analysis. The “borrowed strength” density estimation (BSDE) method via mixture models enables one to estimate the local probability density function in a random field wherein potential similarities between the density functions for the subregions are exploited. This article proposes an efficient methods for SSD estimation by integrating the borrowed strength technique into the alternative EM framework which combines the statistical basis of the BSDE approach with the stability and improved convergence rate of the alternative EM methods. In addition, we propose adaptive SSD estimation methods that extend the aforementioned approach by eliminating the need to find the posterior probability of membership of the component densities afresh in each subregion. Simulation results and an application to the detection and identification of man-made regions of interest in an unmanned aerial vehicle imagery experiment show that the adaptive methods significantly outperform the BSDE method. Other applications include automatic target recognition, mammographic image analysis, and minefield detection. 相似文献
170.
A novel strategy for constructing multiple joined genes of acidic partner-mediated antimicrobial peptide is described. This
strategy allows the expression of antimicrobial peptide byEscherichia coli in a stable form and with high yield. Cecropin A (1–8)-melittin (1–10) (CAME) hybrid peptide was selected as a model of antimicrobial
peptide. An acidic fragment from magainin intervening sequence was fused to the antimicrobial peptide as a partner to neutralize
the lethal effects on the host cells. Multiple copies of the fusion peptide gene were tandemly linked and cloned into the
expression vector pET21a. Multimers were expressed at high levels, reaching up to 36% of total cell proteins, and expression
levels were proportional to the degree of multimerization. The fusion proteins were mainly expressed as inclusion bodies,
probably owing to cysteine residues in the multimers. The target CAME peptide was obtained by cleaving the multimers with
cyanogen bromide and purified by cation-exchange chromatography. Recombinant CAME peptide showed strong antimicrobial activities
against both Gram-negative and -positive bacteria. These results might provide an efficient solution for high-level expression
of various kinds of antimicrobial peptides that are toxic to the host. 相似文献