Mycoplasma infection of cultured cells

Mycoplasma contamination is tough to detect and even more difficult to eradicate. It is best to start over fresh from clean cell stocks, but several elimination options are available.     

Genetic imprinting suggested by maternal heterodisomy in nondeletion Prader-Willi syndrome

Prader-Willi syndrome (PWS) is the most common form of dysmorphic genetic obesity associated with mental retardation. About 60% of cases have a cytological deletion of chromosome 15q11q13 (refs 2, 3). These deletions occur de novo exclusively on the paternal chromosome. By contrast, Angelman syndrome (AS) is a very different clinical disorder and is also associated with deletions of region 15q11q13 (refs 6-8), indistinguishable from those in PWS except that they occur de novo on the maternal chromosome. The parental origin of the affected chromosomes 15 in these disorders could, therefore, be a contributory factor in determining their clinical phenotypes. We have now used cloned DNA markers specific for the 15q11q13 subregion to determine the parental origin of chromosome 15 in PWS individuals not having cytogenetic deletions; these individuals account for almost all of the remaining 40% of PWS cases. Probands in two families displayed maternal uniparental disomy for chromosome 15q11q13. This is the first demonstration that maternal heterodisomy--the presence of two different chromosome 15s derived from the mother--can be associated with a human genetic disease. The absence of a paternal contribution of genes in region 15q11q13, as found in PWS deletion cases, rather than a mutation in a specific gene(s) in this region may result in expression of the clinical phenotype. Thus, we conclude that a gene or genes in region 15q11q13 must be inherited from each parent for normal human development.     

Substitution at residue 227 of H-2 class I molecules abrogates recognition by CD8-dependent, but not CD8-independent, cytotoxic T lymphocytes

The CD8 (Lyt 2) molecule is a phenotypic marker for T lymphocytes that recognize and react with major histocompatibility complex (MHC) class I molecules. Antibody blocking experiments and gene transfection studies indicate that CD8 binds to a determinant on MHC class I molecules on the target cells, facilitating interaction between effector T lymphocytes and the target cell. The CD8 molecule may also be involved in transmembrane signalling during T-cell activation. The existence of CD8- cytotoxic T lymphocytes (CTL) and class I-reactive CTL that are not inhibited by antibody to CD8 suggests that at least some CTL do not require the CD8 molecule to interact with and lyse target cells. We have recently demonstrated that cells transfected with an H-2Dd gene that carries a mutation at residue 227 are not killed by primary CTL8. Here we show that although this mutation abrogates recognition by primary CTL, it does not affect recognition by CD8-independent CTL, suggesting that residue 227 of class I molecules might contribute to a determinant that is the ligand of the CD8 molecule.     

Three-dimensional crystal structures of Escherichia coli met repressor with and without corepressor

The three-dimensional crystal structure of met repressor, in the presence or absence of bound corepressor (S-adenosylmethionine), shows a dimer of intertwined monomers, which do not have the helix-turn-helix motif characteristic of other bacterial repressor and activator structures. We propose that the interaction of met repressor with DNA occurs through either a pair of symmetry-related alpha-helices or a pair of beta-strands, and suggest a model for binding of several dimers to met operator regions.     

适用于动态有向图路径检索的一种数据结构

给出一种表达加权有向图的数据结构，它使得对此有向图进行“插入”操作后，只需进行Ｏ（ｎ２）时间的维护工作，就可使得每对结点间的最短路径迅速地得到修整。     

鲁棒极点配置方法

研究一类线性多变量系统的鲁棒极点配置问题，提出了一种基于极点配置和目标函数优化的鲁棒极点配置方法。基本思想是，利用极点配置的参数化表示结果，以系统输出的Ｌ∞范数作为极点配置寻优的准则函数，通过解优化问题的途径确定极点配置问题中的自由参数。     

正交射流燃烧器气固两相流动的数值计算

运用气相ｋ－ε模型和颗粒相代数方程模型对正交射流煤粉燃烧器气固两相流场进行了数值模拟，获得了该燃烧器内的气、固两相速度分布，颗粒质量流分布，并与实验值进行了对比，两者定性符合，同时，探讨了颗粒直径对颗粒混合的影响，得到了一些很有价值的结论。     

PMSM伺服控制的数字电流环研究

研究了永磁同步电动机（ＰＭＳＭ）伺服系统的一种新型数字电流环方案，该方案采用了规则采样法生成ＰＷＭ波的比例型电流调节器，提出用前馈补偿和变电流环增益技术才能提高电流调节性能，给出了数字仿真和实验结果。     

基于灰度与边缘的图像分割方法

提出一种基于多图像信息的图像分割方法，利用Ｂａｙｅｓ分类准则，根据每个像素的多图像信息向量将其分为目标或背景，并对动态图像组成的图像序列或静态图像的分割给出了不同的像素分类准则，同时给出了硬件实时实现的原理，该方法适用于图像序列、低对比度图像和其它难于用一种图像信息分割的图像。实验证明了该方法的有效性。