We report solid-state 17O NMR determination of the 17O NMR tensors for the keto carbonyl oxygen (O6) of guanine in two 17O-enriched guanosine derivatives: [6-17O]guanosine (G1) and 2',3',5'-O-triacetyl-[6-17O]guanosine (G2). In G1.2H2O, guanosine molecules form hydrogen-bonded G-ribbons where the guanine bases are linked by O6...H-N2 and N7...H-N7 hydrogen bonds in a zigzag fashion. In addition...

Phosphoramidite reagents can phosphitylate guanine bases at the O6-position during solid phase synthesis and serious chain cleavage occurs if the base phosphitylation is not eliminated before the iodine/water oxidation step. This can be accomplished by blocking the O6-position with a 2-cyanoethyl protecting group for deoxyribonucleotides or with a p-nitrophenylethyl group for ribonucleotides, r...

Two cell lines, one proficient (Mex+) and one deficient (Mex-) in the ability to remove O6-methylguanine, have been isolated by Epstein-Barr virus-mediated transformation of a single blood sample obtained from a normal human male. Extracts of untreated cells differ in their O6-methylguanine transferase (methyl acceptor protein) activity. Although both lines arise from the same individual, they ...

Type IIA flux compactifications with O6-planes have been argued from a four dimensional effective theory point of view to admit stable, moduli free solutions. We discuss in detail the ten dimensional description of such vacua and present exact supersymmetric solutions in the case when the O6-charge is smoothly distributed: the geometry is Calabi-Yau and the dilaton is constant. In the localized...

Ten out of 18 babies at risk developed enteritis in an outbreak in a special-care baby unit. Salmonella, Shigella, and Escherichia coli belonging to the traditional infantile enteropathogenic serogroups were not found in faeces from the babies and the staff, and no virus particles were found by electron microscopy. Detailed serotyping of E. coli showed that five of the 10 babies with diarrhoea ...

The most important risk factors for anxiety disorders include genes, early life stress, and current stress. These factors do not act independently but interact with each other throughout human development through examples such as epigenetic modifications and complex forms of learning. The neural substrate of pathological anxiety includes hyperactivity in the amygdala and other limbic brain regi...