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81.
A cytoplasmic dynein ATPase has been identified in three species of unfertilized sea urchin eggs, Strongylocentrotus droebachiensis, S. purpuratus, and Arbacia punctulata. The enzyme was partially purified by sucrose gradient density centrifugation, and its polypeptide chain weight and composition were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The protein has enzymatic characteristics in common with flagellar dynein. It is activated nearly equally by Mg2+ and Ca2+, has no activity in the presence of K+ and EDTA, shows a specificity for ATP over other nucleoside triphosphates, and is inhibited by vanadate anion. On SDS-PAGE, the enzyme shows two major bands at 320,000 and 385,000 daltons, comigrating with certain ciliary and flagellar dynein polypeptides. The enzyme, given the name “egg dynein,” constitutes 2 to 4% of the total cell protein in the unfertilized egg and maintains this high value from fertilization through the late blastula stage. It appears to be equally distributed throughout the embryo at the 16-cell stage. Possible functions of egg dynein are discussed and models for dynein-microtubule mediated movements within the cytoplasm are presented. 相似文献
82.
Some aspects of sociosexual behavior and the age at which maturing females experienced their first evident pregnancy and at
which maturing males caused their first evident pregnancy were recorded in Saguinus fuscicolliscohabiting from 6 months of age with either an adult or a maturing sex partner. The following pair combinations and trios
were studied: young male -young female, young male-adult female, adult male-young female, and adult male-young male-young
female. The most frequent type of social interaction between young animals was rough and tumble play, while huddling was the
most frequent interaction between young animals and their adult partners. Grooming and sexual interactions were very infrequent
and there were no differences in the frequencies of these interactions among subject groups. Maturing females cohabiting with
an adult male conceived significantly earlier than maturing females cohabiting with a male of their own age. Maturing males
cohabiting with adult females sired offspring at a significantly earlier age than males cohabiting with a female of their
own age. Some possible behavioral and physiological processes involved in the causation of early reproductive success in young
tamarins cohabiting with adults are discussed.
Saguinus fuscicollis fuscicollis andSaguinus fuscicollis illigeri. 相似文献
83.
Yair Parag 《American journal of botany》1968,55(8):984-988
Pairs of nuclei in apical cells of a common-B heterokaryon (A41 B41 + A2 B41) of Schizophyllum commune fused prior to the nuclear division. It is assumed that each fusion was followed by a reduction division. Five consecutive fusions and divisions in a single hypha were photographed in situ with a phase microscope. These fusions and reduction divisions are possibly related to the genetically determined phenomenon of somatic recombination as a part of the parasexual cycle in fungi. 相似文献
84.
L. C. Vining S. E. Jensen D. W. S. Westlake Y. Aharonowitz S. Wolfe 《Applied microbiology and biotechnology》1987,27(3):240-246
Summary The relationships between growth, cephamycin production and isopenicillin N synthetase (IPNS) activity in cultures of Streptomyces clavuligerus were examined to establish conditions that optimize the yield and specific activity of the enzyme. Unexpectedly for a secondary metabolic pathway component, IPNS was synthesized preferentially during rapid growth and reached its maximum specific activity in cultures supplied with readily assimilated sources of nitrogen. The activity decreased sharply as cultures entered stationary phase. On the other hand, comparisons of growth and antibiotic production on a range of carbon and nitrogen sources as well as measurements of IPNS activity in chemostat cultures implicated catabolite repression, a mechanism usually associated with separation of trophophase and idiophase activities, as an important factor in controlling expression of the secondary metabolic pathway. An explanation for the timing of IPNS biosynthesis is suggested.Dedicated to Professor H. J. Rehm on the occasion of his 60th birthday 相似文献
85.
Robert Greenberg Daniel Lundell Yair Alroy Susan Bonitz Russell Condon James Fossetta Beth Frommer Keith Gewain Mitchell Katz Paul J. Leibowitz Dr. satwant K. Narula Robert Kastelein Anita Van Kimmenade 《Current microbiology》1988,17(6):321-332
Human granulocyte-macrophage colony stimulating factor (HuGM-CSF) was expressed periplasmically inEscherichia coli with the secretory vector, pINIIIompA2 [10]. HuGM-CSF protein thus expressed was shown to be faithfully cleaved and biologically active. This protein, however, could not be released by osmotic shock and, on subcellular fractionation, co-sedimented with the outer membrane fraction. The effect of promoters, vectors, host strains, induction conditions and media formulation on expression levels was also evaluated. Some of these factors play a significant role in determining maximal achievable levels of HuGM-CSF in the secretory expression system ofE. coli.Both may be considered first authors. 相似文献
86.
The three chthamalids Chthamalus stellatus , C. montagui and Euraphia depressa are common inhabitants of the intertidal zone in the Eastern Atlantic, Mediterranean Sea and Black Sea. In this study, we investigated the occurrence of these barnacles in a wide range of their distribution. Population divergences of these two species have been inferred using three molecular markers — internal transcribed spacer (ITS), elongation factor 1α (EF-1α) and cytochrome oxidase subunit I (COI). ITS sequences of C. stellatus were identical throughout the species range, whereas ITS sequences of C. montagui indicated that the Black Sea and Mediterranean populations are isolated from the Atlantic population. The COI and EF-1α sequences were the most variable and informative. They indicated a high genetic divergence between Atlantic, Mediterranean and Black Sea populations for C. montagui . In addition significant genetic structure was found among the populations of C. stellatus based on EF-1α but not COI. Interestingly, our molecular dating analysis correlated the pattern of diversification in C. montagui to major geological changes that occurred in the Mediterranean during the end of the Messinian and Pleiocene periods. We suggest that palaeohistory shaped the divergences between Chthamalus populations that have probably been maintained by current hydrographic conditions. Finally, COI phylogenetic analysis placed the genus Euraphia within the Chthamalus clade, suggesting the need for a taxonomic revision of Euraphia . This study represents the most detailed phylogeographical analysis of intertidal Mediterranean species to date, and shows that geological events have strongly shaped the current diversity pattern of this fauna. 相似文献
87.
Individualized treatment regimes (ITRs) aim to recommend treatments based on patient‐specific characteristics in order to maximize the expected clinical outcome. Outcome weighted learning approaches have been proposed for this optimization problem with primary focus on the binary treatment case. Many require assumptions of the outcome value or the randomization mechanism. In this paper, we propose a general framework for multicategory ITRs using generic surrogate risk. The proposed method accommodates the situations when the outcome takes negative value and/or when the propensity score is unknown. Theoretical results about Fisher consistency, excess risk, and risk consistency are established. In practice, we recommend using differentiable convex loss for computational optimization. We demonstrate the superiority of the proposed method under multinomial deviance risk to some existing methods by simulation and application on data from a clinical trial. 相似文献
88.
Cohen S Shoshana OY Zelman-Toister E Maharshak N Binsky-Ehrenreich I Gordin M Hazan-Halevy I Herishanu Y Shvidel L Haran M Leng L Bucala R Harroch S Shachar I 《Journal of immunology (Baltimore, Md. : 1950)》2012,188(1):259-269
Lasting B cell persistence depends on survival signals that are transduced by cell surface receptors. In this study, we describe a novel biological mechanism essential for survival and homeostasis of normal peripheral mature B cells and chronic lymphocytic leukemia cells, regulated by the heparin-binding cytokine, midkine (MK), and its proteoglycan receptor, the receptor-type tyrosine phosphatase ζ (RPTPζ). We demonstrate that MK initiates a signaling cascade leading to B cell survival by binding to RPTPζ. In mice lacking PTPRZ, the proportion and number of the mature B cell population are reduced. Our results emphasize a unique and critical function for MK signaling in the previously described MIF/CD74-induced survival pathway. Stimulation of CD74 with MIF leads to c-Met activation, resulting in elevation of MK expression in both normal mouse splenic B and chronic lymphocytic leukemia cells. Our results indicate that MK and RPTPζ are important regulators of the B cell repertoire. These findings could pave the way toward understanding the mechanisms shaping B cell survival and suggest novel therapeutic strategies based on the blockade of the MK/RPTPζ-dependent survival pathway. 相似文献
89.
Evidence for a specific microwave radiation effect on the green fluorescent protein 总被引:1,自引:0,他引:1
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We have compared the effect of microwave irradiation and of conventional heating on the fluorescence of solution-based green fluorescent protein. A specialized near-field 8.5 GHz microwave applicator operating at 250 mW input microwave power was used. The solution temperature, the intensity, and the spectrum of the green fluorescent protein fluorescence 1), under microwave irradiation and 2), under conventional heating, were measured. In both cases the fluorescence intensity decreases and the spectrum becomes red-shifted. Although the microwave irradiation heats the solution, the microwave-induced changes in fluorescence cannot be explained by heating alone. Several possible scenarios are discussed. 相似文献
90.