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141.
C. Loštický 《Cellular and molecular life sciences : CMLS》1969,25(10):1034-1034
Zusammenfassung Es wurden Interaktionen von Protamin mit vorher in Agar-Gel elektrophoretisch getrennten plasmatischen Eiweisskörpern untersucht. Neben der schon früher bekannten Interaktion mit Fibrinogen wurden auch solche mit beiden Klassen der plasmatischen Lipoproteine gefunden. 相似文献
142.
真空冷冻干燥技术在生物材料制备中的应用与进展 总被引:4,自引:0,他引:4
黎先发 《西南科技大学学报》2004,19(2):117-121
介绍了真空冷冻干燥的基本原理及其特点,简要综述了真空冷冻干燥技术在生物材料制备的应用及发展概况。 相似文献
143.
罗先发 《吉首大学学报(自然科学版)》1998,19(1):51-55
得到实Banach空间X的闭有限余维子空间是伪半Chebyshev的特征,由此得到X*的弱*闭有限余维子空间是伪Chebyshev的特征,把这些结果用到数列空间,得到更简明的结果。 相似文献
144.
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146.
The breast cancer susceptibility protein BRCA2 controls the function of RAD51, a recombinase enzyme, in pathways for DNA repair by homologous recombination. We report here the structure of a complex between an evolutionarily conserved sequence in BRCA2 (the BRC repeat) and the RecA-homology domain of RAD51. The BRC repeat mimics a motif in RAD51 that serves as an interface for oligomerization between individual RAD51 monomers, thus enabling BRCA2 to control the assembly of the RAD51 nucleoprotein filament, which is essential for strand-pairing reactions during DNA recombination. The RAD51 oligomerization motif is highly conserved among RecA-like recombinases, highlighting a common evolutionary origin for the mechanism of nucleoprotein filament formation, mirrored in the BRC repeat. Cancer-associated mutations that affect the BRC repeat disrupt its predicted interaction with RAD51, yielding structural insight into mechanisms for cancer susceptibility. 相似文献
147.
VEGFR1-positive haematopoietic bone marrow progenitors initiate the pre-metastatic niche 总被引:4,自引:0,他引:4
Kaplan RN Riba RD Zacharoulis S Bramley AH Vincent L Costa C MacDonald DD Jin DK Shido K Kerns SA Zhu Z Hicklin D Wu Y Port JL Altorki N Port ER Ruggero D Shmelkov SV Jensen KK Rafii S Lyden D 《Nature》2005,438(7069):820-827
The cellular and molecular mechanisms by which a tumour cell undergoes metastasis to a predetermined location are largely unknown. Here we demonstrate that bone marrow-derived haematopoietic progenitor cells that express vascular endothelial growth factor receptor 1 (VEGFR1; also known as Flt1) home to tumour-specific pre-metastatic sites and form cellular clusters before the arrival of tumour cells. Preventing VEGFR1 function using antibodies or by the removal of VEGFR1(+) cells from the bone marrow of wild-type mice abrogates the formation of these pre-metastatic clusters and prevents tumour metastasis, whereas reconstitution with selected Id3 (inhibitor of differentiation 3)-competent VEGFR1+ cells establishes cluster formation and tumour metastasis in Id3 knockout mice. We also show that VEGFR1+ cells express VLA-4 (also known as integrin alpha4beta1), and that tumour-specific growth factors upregulate fibronectin--a VLA-4 ligand--in resident fibroblasts, providing a permissive niche for incoming tumour cells. Conditioned media obtained from distinct tumour types with unique patterns of metastatic spread redirected fibronectin expression and cluster formation, thereby transforming the metastatic profile. These findings demonstrate a requirement for VEGFR1+ haematopoietic progenitors in the regulation of metastasis, and suggest that expression patterns of fibronectin and VEGFR1+VLA-4+ clusters dictate organ-specific tumour spread. 相似文献
148.
Although it is widely accepted that most galaxies have supermassive black holes at their centres, concrete proof has proved elusive. Sagittarius A* (Sgr A*), an extremely compact radio source at the centre of our Galaxy, is the best candidate for proof, because it is the closest. Previous very-long-baseline interferometry observations (at 7 mm wavelength) reported that Sgr A* is approximately 2 astronomical units (au) in size, but this is still larger than the 'shadow' (a remarkably dim inner region encircled by a bright ring) that should arise from general relativistic effects near the event horizon of the black hole. Moreover, the measured size is wavelength dependent. Here we report a radio image of Sgr A* at a wavelength of 3.5 mm, demonstrating that its size is approximately 1 au. When combined with the lower limit on its mass, the lower limit on the mass density is 6.5 x 10(21)M(o) pc(-3) (where M(o) is the solar mass), which provides strong evidence that Sgr A* is a supermassive black hole. The power-law relationship between wavelength and intrinsic size (size proportional, variantwavelength(1.09)) explicitly rules out explanations other than those emission models with stratified structure, which predict a smaller emitting region observed at a shorter radio wavelength. 相似文献
149.
Polyalanine expansion and frameshift mutations of the paired-like homeobox gene PHOX2B in congenital central hypoventilation syndrome 总被引:20,自引:0,他引:20
Amiel J Laudier B Attié-Bitach T Trang H de Pontual L Gener B Trochet D Etchevers H Ray P Simonneau M Vekemans M Munnich A Gaultier C Lyonnet S 《Nature genetics》2003,33(4):459-461
Congenital central hypoventilation syndrome (CCHS or Ondine's curse; OMIM 209880) is a life-threatening disorder involving an impaired ventilatory response to hypercarbia and hypoxemia. This core phenotype is associated with lower-penetrance anomalies of the autonomic nervous system (ANS) including Hirschsprung disease and tumors of neural-crest derivatives such as ganglioneuromas and neuroblastomas. In mice, the development of ANS reflex circuits is dependent on the paired-like homeobox gene Phox2b. Thus, we regarded its human ortholog, PHOX2B, as a candidate gene in CCHS. We found heterozygous de novo mutations in PHOX2B in 18 of 29 individuals with CCHS. Most mutations consisted of 5-9 alanine expansions within a 20-residue polyalanine tract probably resulting from non-homologous recombination. We show that PHOX2B is expressed in both the central and the peripheral ANS during human embryonic development. Our data support an essential role of PHOX2B in the normal patterning of the autonomous ventilation system and, more generally, of the ANS in humans. 相似文献
150.
孟宪法 《山东科技大学学报(自然科学版)》1987,(2)
本文用可靠性理论,分析了综合机械化工作面产量、劳动生产率、成本与可靠性之间的关系,探讨了提高综合机械化工作面可靠性的主要途径。 相似文献