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1.
This paper is concerned with gene survival in a population which may increase without density dependence according to a generalization of the Moran model for haploid individuals. A selective advantage to one allele and the possibility of differential reproductive rates are allowed. Simple conditions are given for ultimate homozygosity to be certain and for the possibility of ultimate polymorphism. The results complement and extend those of Heyde (1981, 1982). 相似文献
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A putative GDP–GTP exchange factor is required for development of the excretory cell in Caenorhabditis elegans
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Norio Suzuki Matthew Buechner Kiyoji Nishiwaki David H. Hall Hiroyuki Nakanishi Yoshimi Takai Naoki Hisamoto Kunihiro Matsumoto 《EMBO reports》2001,2(6):530-535
The Caenorhabditis elegans excretory cell extends tubular processes, called canals, along the basolateral surface of the epidermis. Mutations in the exc-5 gene cause tubulocystic defects in this canal. Ultrastructural analysis suggests that exc-5 is required for the proper placement of cytoskeletal elements at the apical epithelial surface. exc-5 encodes a protein homologous to guanine nucleotide exchange factors and contains motif architecture similar to that of FGD1, which is responsible for faciogenital dysplasia. exc-5 interacts genetically with mig-2, which encodes Rho GTPase. These results suggest that EXC-5 controls the structural organization of the excretory canal by regulating Rho family GTPase activities. 相似文献
3.
Difficulties were encountered with the orcein method currently being used to demonstrate hepatitis B surface antigen and copper-associated protein in the liver when a new batch of dye was introduced. A survey of published material produced a plethora of methods with many contradictory recommendations. A number of methods and a variety of orceins were compared to determine which methods and orcein solutions would give the most consistent results. Two methods gave equally satisfactory results and can be recommended for routine use in screening paraffin sections of liver for hepatitis B surface antigen and copper-associated protein. 相似文献
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Summary The physicochemical properties of the interactions of RNA polymerase (RPase) with promoter and nonspecific DNA sequences have been investigated. These show that nonspecific binding is principally an ionic interaction and that promoter binding is more complex, involving nonionic interactions. Nonspecific binding has been shown to be very important in the promoter search, and one-dimensional diffusion can account for the rate at which RPase finds the promoter. Significant differences have been reported in the binding process for various promoters and in the effects of regulatory proteins. Further investigation of these differences will lead to a better understanding of the selectivity and regulation of the initiation process.The pathways of the initiation process have been outlined, by recent studies and considerable progress has been made in determining the rates of interconversion of the intermediate states. A number of questions remain about the detail of initiation and the effects of various parameters on the reactions. Of particular importance is the identification of the point at which the enzyme becomes truly processive. In addition, the step which is rate limiting has not been identified in either the productive or nonproductive process. The mechanistic features of the steps after bond formation are just beginning to yield to investigation.Use of substrate analogs with RPase has led to a picture of the polymerization site according to the ability of the enzyme to incorporate analogs. Base specificity appears to be determined primarily by interaction with the template rather than the enzyme, but the ribose moiety must interact with the site quite specifically. The orientation of the phosphate residues has been determined by NMR, which has also proved to be a valuable probe of the initiation site. At this site base specificity is resident in the enzyme and expressed through the interaction of the base and intrinsic metal, as shown by studies with the Cobalt substituted enzyme. In both initiation and polymerization, the reaction has been shown to proceed by inversion of configuration. Techniques similar to those used for initiation will probably be applied to the polymerization reaction as well, which has not recently received as much attention with respect to mechanism. Functional phenomena such as pausing make the polymerization process particularly promising for producing insight into RPase reactions. 相似文献
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P Kendall-Taylor K Hall D G Johnston R W Prescott 《BMJ (Clinical research ed.)》1982,285(6340):465-467
The effect of pergolide mesylate was studied in two previously untreated men with large prolactinomas and exceptionally high prolactin concentrations. The study was designed to determine whether pergolide would be effective in alleviating symptoms, correcting hormonal abnormalities and shrinking the tumour. Starting with 50 micrograms daily the dose of pergolide was slowly increased over 10 weeks to 1 mg once daily, when repeat assessment was performed. Both patients reported complete relief of symptoms, with no side effects. Serum prolactin concentration was suppressed to normal in both subjects, and evidence to suggest tumour shrinkage was observed. Pergolide appears to be effective treatment for men with large prolactinomas. 相似文献
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M Hall D K Parker P L Grover J Y Lu N E Hopkins W L Alworth 《Chemico-biological interactions》1990,76(2):181-192
The effects of three aryl acetylenes, 1-ethynylpyrene (EP), 2-ethynylnaphthalene (EN) and 3-ethynylperylene (EPE), upon the metabolism of benzo[a]pyrene (BaP) by microsomes isolated from rat liver were investigated. These aryl acetylenes all inhibited the total metabolism of BaP. Formation of BaP 7,8-dihydrodiol and BaP tetrol products by microsomal preparations from rats that had been pretreated with 3-methylcholanthrene (3MC) were preferentially inhibited. The effects of EP upon the metabolism of BaP 7,8-dihydrodiol by microsomes from rat liver were also studied. This aryl acetylene strongly inhibited the formation of BaP tetrols from BaP 7,8-dihydrodiol by liver microsomes both from untreated rats and from rats pretreated with 3MC, but enhanced the conversion of the BaP dihydrodiol into other metabolites. 相似文献
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