Submicrometer Superconducting YBa2Cu3O6+x Particles Made by a Low-Temperature Synthetic Route     

Horowitz HS  McLain SJ  Sleight AW  Druliner JD  Gai PL  Vankavelaar MJ  Wagner JL  Biggs BD  Poon SJ 《Science (New York, N.Y.)》1989,243(4887):66-69

Evidence suggests that superconducting, orthorhombic YBa(2)Cu(3)O(6+x)+ (x greater, similar 0.5) is always produced by oxidation of the oxygen-deficient, tetragonal form (x less, similar 0.5) of this phase (commonly referred to as 123). A synthetic route whereby solution-derived, carbon-free precursors are decomposed at 650 degrees to 700 degrees C in inert atmosphere to yield tetragonal 123 is now available. Appropriate precursors include hydrated oxides derived from the hydrolysis of organometallic solutions and aqueous solution-derived hyponitrites. Subsequent oxidation of the tetragonal phase at 400 degrees C results in submicrometer particles of orthorhombic 123. Superconductivity (T(c) onset approximately 87 K) has been confirmed in these materials by both Meissner effect and specific-heat measurements.  相似文献   

Oxygen-18 enrichment of planktonic foraminifera due to gametogenic calcification below the euphotic zone     

Blanc PL  Bé AW 《Science (New York, N.Y.)》1981,213(4513):1247-1250

Empty shells of spinose planktonic foraminifera on the seabed are significantly enriched in oxygen-18 as compared with the shells of their living counterparts in surface waters. This enrichment is due to gametogenic calcification, which extracts calcium carbonate from deeper and colder waters as the shell sinks below the euphotic zone. JEAN-CLAUDE DUPLESSY.  相似文献   

Picosecond kinetics of events leading to reaction center bacteriochlorophyll oxidation     

Kaufmann KJ  Dutton PL  Netzel TL  Leigh JS  Rentzepis PM 《Science (New York, N.Y.)》1975,188(4195):1301-1304

A transient absorption spectrum has been measured in Rhodopseudomonas spheroides R26 reaction centers. Its salient features indicate that both the bacteriopheophytin and bacteriochlorophyll chromophores play a role in the excited state. Decay of this state yields a rise time for oxidation of the reaction center complex of about 150 picoseconds.  相似文献   

A NOTE ON THE SURFACE VISCOSITY OF COLLOIDAL SOLUTIONS     

Du Noöo PL 《Science (New York, N.Y.)》1925,61(1570):117-118

  相似文献   

BRCA2 function in DNA binding and recombination from a BRCA2-DSS1-ssDNA structure   总被引：1，自引：0，他引：1  

Yang H  Jeffrey PD  Miller J  Kinnucan E  Sun Y  Thoma NH  Zheng N  Chen PL  Lee WH  Pavletich NP 《Science (New York, N.Y.)》2002,297(5588):1837-1848

Mutations in the BRCA2 (breast cancer susceptibility gene 2) tumor suppressor lead to chromosomal instability due to defects in the repair of double-strand DNA breaks (DSBs) by homologous recombination, but BRCA2's role in this process has been unclear. Here, we present the 3.1 angstrom crystal structure of a approximately 90-kilodalton BRCA2 domain bound to DSS1, which reveals three oligonucleotide-binding (OB) folds and a helix-turn-helix (HTH) motif. We also (i) demonstrate that this BRCA2 domain binds single-stranded DNA, (ii) present its 3.5 angstrom structure bound to oligo(dT)9, (iii) provide data that implicate the HTH motif in dsDNA binding, and (iv) show that BRCA2 stimulates RAD51-mediated recombination in vitro. These findings establish that BRCA2 functions directly in homologous recombination and provide a structural and biochemical basis for understanding the loss of recombination-mediated DSB repair in BRCA2-associated cancers.  相似文献   

Mycobacterial Ku and ligase proteins constitute a two-component NHEJ repair machine     

Della M  Palmbos PL  Tseng HM  Tonkin LM  Daley JM  Topper LM  Pitcher RS  Tomkinson AE  Wilson TE  Doherty AJ 《Science (New York, N.Y.)》2004,306(5696):683-685

In mammalian cells, repair of DNA double-strand breaks (DSBs) by nonhomologous end-joining (NHEJ) is critical for genome stability. Although the end-bridging and ligation steps of NHEJ have been reconstituted in vitro, little is known about the end-processing reactions that occur before ligation. Recently, functionally homologous end-bridging and ligation activities have been identified in prokarya. Consistent with its homology to polymerases and nucleases, we demonstrate that DNA ligase D from Mycobacterium tuberculosis (Mt-Lig) possesses a unique variety of nucleotidyl transferase activities, including gap-filling polymerase, terminal transferase, and primase, and is also a 3' to 5' exonuclease. These enzyme activities allow the Mt-Ku and Mt-Lig proteins to join incompatible DSB ends in vitro, as well as to reconstitute NHEJ in vivo in yeast. These results demonstrate that prokaryotic Ku and ligase form a bona fide NHEJ system that encodes all the recognition, processing, and ligation activities required for DSB repair.  相似文献   

Molecular biology. When a part is as good as the whole     

deHaseth PL  Nilsen TW 《Science (New York, N.Y.)》2004,303(5662):1307-1308

  相似文献   

Triallelic inheritance in Bardet-Biedl syndrome, a Mendelian recessive disorder   总被引：1，自引：0，他引：1  

Katsanis N  Ansley SJ  Badano JL  Eichers ER  Lewis RA  Hoskins BE  Scambler PJ  Davidson WS  Beales PL  Lupski JR 《Science (New York, N.Y.)》2001,293(5538):2256-2259

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder characterized by multiple clinical features that include pigmentary retinal dystrophy, polydactyly, obesity, developmental delay, and renal defects. BBS is considered an autosomal recessive disorder, and recent positional cloning efforts have identified two BBS genes (BBS2 and BBS6). We screened our cohort of 163 BBS families for mutations in both BBS2 and BBS6 and report the presence of three mutant alleles in affected individuals in four pedigrees. In addition, we detected unaffected individuals in two pedigrees who carry two BBS2 mutations but not a BBS6 mutation. We therefore propose that BBS may not be a single-gene recessive disease but a complex trait requiring three mutant alleles to manifest the phenotype. This triallelic model of disease transmission may be important in the study of both Mendelian and multifactorial disorders.  相似文献   

Fatty acids in eleven species of blue-green algae: geochemical significance     

Parker PL  Van Baalen C  Maurer L 《Science (New York, N.Y.)》1967,155(3763):707-708

Analyses of the total lipids of 11 species of blue-green algae showed a simple but qualitatively variable fatty acid composition. The species can be grouped in three categories on the basis of their oleic, linoleic, and linolenic acid content. One species was unusual in that the ten-carbon acid accounts for one-half of its total fatty acid. Branched chain acids are absent in the algae, but are major components of marine bacteria. The geochemical significance of the data is discussed.  相似文献   

Chemical carcinogens     

Grover PL 《Science (New York, N.Y.)》1979,204(4399):1301

  相似文献