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11.
The ability of liposomes composed of different kinds of phospholipid materials to adhere to the surface of the cornea was studied in the rabbit. The liposomes were labelled with tracer amounts of an I125-labelled phosphatidylethanolamine derivative and were instilled in 10 microliters drops onto the cornea. The retention of radioactivity was monitored. The results show that liposomes containing positively charged phospholipids are better retained than an albumin control. Thus, it may be possible to develop a drug delivery liposome system which would permit long-term sustained release of ophthalmic drugs onto the cornea. 相似文献
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C J Brown R G Lafreniere V E Powers G Sebastio A Ballabio A L Pettigrew D H Ledbetter E Levy I W Craig H F Willard 《Nature》1991,349(6304):82-84
X-chromosome inactivation results in the strictly cis-limited inactivation of many but not all genes on one of the two X chromosomes during early development in somatic cells of mammalian females. One feature of virtually all models of X inactivation is the existence of an X-inactivation centre (XIC) required in cis for inactivation to occur. This concept predicts that all structurally abnormal X chromosomes capable of being inactivated have in common a defineable region of the X chromosome. Here we report an analysis of several such rearranged human X chromosomes and define a minimal region of overlap. The results are consistent with models invoking a single XIC and provide a molecular foothold for cloning and analysing the XIC region. One of the markers that defines this region is the XIST gene, which is expressed specifically from inactive, but not active, X chromosomes. The localization of the XIST gene to the XIC region on the human X chromosome implicates XIST in some aspect of X inactivation. 相似文献
13.
We propose a development stemming from Roux (1988). The principle is progressively to modify the dissimilarities so that every quadruple satisfies not only the additive inequality, as in Roux's method, but also all triangle inequalities. Our method thus ensures that the results are tree distances even when the observed dissimilarities are nonmetric. The method relies on the analytic solution of the least-squares projection onto a tree distance of the dissimilarities attached to a single quadruple. This goal is achieved by using geometric reasoning which also enables an easy proof of algorithm's convergence. This proof is simpler and more complete than that of Roux (1988) and applies to other similar reduction methods based on local least-squares projection. The method is illustrated using Case's (1978) data. Finally, we provide a comparative study with simulated data and show that our method compares favorably with that of Studier and Keppler (1988) which follows in the ADDTREE tradition (Sattath and Tversky 1977). Moreover, this study seems to indicate that our method's results are generally close to the global optimum according to variance accounted for.We offer sincere thanks to Gilles Caraux, Bernard Fichet, Alain Guénoche, and Maurice Roux for helpful discussions, advice, and for reading the preliminary versions of this paper. We are grateful to three anonymous referees and to the editor for many insightful comments. This research was supported in part by the GREG and the IA2 network. 相似文献
14.
Segregation of transferable R factors into Escherichia coli minicells 总被引:18,自引:0,他引:18
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Levskaya A Chevalier AA Tabor JJ Simpson ZB Lavery LA Levy M Davidson EA Scouras A Ellington AD Marcotte EM Voigt CA 《Nature》2005,438(7067):441-442
We have designed a bacterial system that is switched between different states by red light. The system consists of a synthetic sensor kinase that allows a lawn of bacteria to function as a biological film, such that the projection of a pattern of light on to the bacteria produces a high-definition (about 100 megapixels per square inch), two-dimensional chemical image. This spatial control of bacterial gene expression could be used to 'print' complex biological materials, for example, and to investigate signalling pathways through precise spatial and temporal control of their phosphorylation steps. 相似文献
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R. Got Georgette Levy R. Bourrillon 《Cellular and molecular life sciences : CMLS》1959,15(12):480-481
Summary The purity of human chorionic gonadotropin showing an activity of 12,000/mg, is confirmed by immuno-electrophoretic analysis. Characteristic antigenic properties of this hormone are revealed by this method. 相似文献
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Jeanna Schwartz Ruth Levy Nurith Vardinon 《Cellular and molecular life sciences : CMLS》1972,28(9):1097-1098
Résumé Trois types d'hématies humaines sont décrites (fortes, faibles, négatives) selon leur réactivité dans l'adhérence sérologique (agglutination d'hématies humaines, exposées à un couple antigène-anticorps, en présence du complément). Ces différences individuelles sont dues à un récepteur dont la présence sur les hématies positives, est demontrée directement (adsorbtion des réactifs sur les hématies positives) et indirectement (perte de la réactivité par trypsinisation, inhibition de la réaction et préparation de sérums spécifiques anti-récepteur). 相似文献
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