Solution structure of the d(T-C-G-A) duplex at acidic pH. A parallel-stranded helix containing C+ .C, G.G and A.A pairs

The solution structure of the d(T-C-G-A) sequence at acidic pH has been determined by a combination of NMR and molecular dynamics calculations including NOE intensity based refinements. This sequence forms a right-handed parallel-stranded duplex with C+ .C (three hydrogen bonds along Watson-Crick edge), G.G (two symmetry related N2-H.. N3 hydrogen bonds) and A.A (two symmetry related N6-H..N7 hydrogen bonds) homo base-pair formation at acidic pH. The duplex is stabilized by intra-strand base stacking at the C2-G3 step and cross-strand base stacking at the G3-A4 step. The thymine residues on partner strands are directed towards each other and are positioned over the C+ .C base-pair. All four residues adopt anti glycosidic torsion angles and C2'-endo type sugar conformations in the parallel-stranded d(T-C-G-A) duplex which exhibits large changes in twist angles between adjacent steps along the duplex. This study rules out previously proposed models for the structure of the d(T-C-G-A) duplex at acidic pH and supports earlier structural contributions, which established that d(C-G) and d(C-G-A) containing sequences at acidic pH pair through parallel-stranded alignment. We have also monitored hydration patterns in the symmetry related grooves of the parallel-stranded d(T-C-G-A) duplex.     

G. Stanley Hall: A reply to Rosenzweig.

Responds to S. G. Rosenzweig's (1970) comments on J. C. McCullers's (1969) assessment of G. Stanley Hall's influence and questions why Hall is not remembered as well as he logically deserves to be by most American psychologists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Solution structure of a Na cation stabilized DNA quadruplex containing G.G.G.G and G.C.G.C tetrads formed by G-G-G-C repeats observed in adeno-associated viral DNA

We have applied NMR and molecular dynamics computations including intensity based refinement to define the structure of the d(G-G-G-C-T4-G-G-G-C) dodecanucleotide in 100 mM NaCl solution. The G-G-G-C sequence is of interest since it has been found as tandem repeats in the DNA sequence of human chromosome 19. The same G-G-G-C sequence is also seen as islands in adeno-associated virus, a human parvovirus, which is unique amongst eukaryotic DNA viruses in its ability to integrate site-specifically into a defined region of human chromosome 19. The d(G-G-G-C-T4-G-G-G-C) sequence forms a quadruplex in Na cation containing solution through head-to-tail dimerization of two symmetry-related stem-hairpin loops with adjacent strands antiparallel to each other around the quadruplex. The connecting T4 loops are of the lateral type, resulting in a quadruplex structure containing two internal G.G.G.G tetrads flanked by G.C.G.C tetrads. The G(anti).G(syn).G(anti).G(syn) tetrads are formed through dimerization associated hydrogen bonding alignments of a pair of Hoogsteen G(anti).G(syn) mismatch pairs, while the G(anti).C(anti).G(anti).C(anti) tetrads are formed through dimerization associated bifurcated hydrogen bonding alignments involving the major groove edges of a pair of Watson-Crick G.C base-pairs. The quadruplex contains two distinct narrow and two symmetric wide grooves with extensive stacking between adjacent tetrad planes. The structure of the quadruplex contains internal cavities that can potentially accommodate Na cations positioned between adjacent tetrad planes. Three such Na cations have been modeled into the structure of the d(G-G-G-C-T4-G-G-G-C) quadruplex. Finally, we speculate on the potential role of quadruplex formation involving G.G.G.G and G.C.G.C tetrads during the integration of the adeno-associated parvovirus into its target on human chromosome 19, both of which involve stretches of G-G-G-C sequence elements.     

曼内斯曼钢管公司用HFI法生产管道用管的实践

从曼内斯曼钢管公司用高频感应焊接法生产管道用直缝焊管的生产实践出发，对管道用焊管的生产过程，包括原料、炼钢、热轧板带生产以及高频感应焊管生产做了简单的介绍。重点介绍了焊管生产的工艺过程及生产设备，并对我国高频直缝焊管机组的改造做了粗浅的探讨。     

Roger G. Barker and behavior settings: A commentary.

Observes that R. G. Barker's (see record 1981-04344-001) paper documents and illustrates his approach to science, his lifelong concern with environment–behavior relations, the major influences that have shaped his thought, and the utility of the behavior setting concept. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)