Quadruplex structure of Oxytricha telomeric DNA oligonucleotides.

The telomeres of most eukaryotes contain a repeating G-rich sequence with the consensus d(T/A)1-4G1-8, of which 12-16 bases form a 3' single-strand overhang beyond the telomeric duplex. It has been proposed that these G-rich oligonucleotides associate to form four-stranded structures from one, two or four individual strands and that these structures may be relevant in vivo. The proposed structures contain Hoogsteen base-paired G-quartets, precedent for which has been in the literature for many years. Here we use 1H NMR spectroscopy to study the conformations of the DNA oligonucleotides d(G4T4G4) (Oxy-1.5) and d(G4T4G4T4G4T4G4) (Oxy-3.5) which contain the Oxytricha telomere repeat (T4G4). We find that these molecules fold to form a symmetrical bimolecular and an intramolecular quadruplex, respectively. Both structures have four G-quartets formed from nucleotides that are alternately syn and anti along each strand. This arrangement differs from earlier models in which the strands are alternately all syn or all anti. The T4 loops in Oxy-1.5 are on opposite ends of the quadruplex and loop diagonally across the G-quartet, resulting in adjacent strands being alternately parallel and antiparallel.     

Engineering the third wave of biocatalysis

Over the past ten years, scientific and technological advances have established biocatalysis as a practical and environmentally friendly alternative to traditional metallo- and organocatalysis in chemical synthesis, both in the laboratory and on an industrial scale. Key advances in DNA sequencing and gene synthesis are at the base of tremendous progress in tailoring biocatalysts by protein engineering and design, and the ability to reorganize enzymes into new biosynthetic pathways. To highlight these achievements, here we discuss applications of protein-engineered biocatalysts ranging from commodity chemicals to advanced pharmaceutical intermediates that use enzyme catalysis as a key step.     

Beta-carotene affects gene expression in lungs of male and female <Emphasis Type="Italic">Bcmo1</Emphasis><Superscript>−/−</Superscript> mice in opposite directions

Molecular mechanisms triggered by high dietary beta-carotene (BC) intake in lung are largely unknown. We performed microarray gene expression analysis on lung tissue of BC supplemented beta-carotene 15,15′-monooxygenase 1 knockout (Bcmo1 ^−/−) mice, which are—like humans—able to accumulate BC. Our main observation was that the genes were regulated in an opposite direction in male and female Bcmo1 ^−/− mice by BC. The steroid biosynthetic pathway was overrepresented in BC-supplemented male Bcmo1 ^−/− mice. Testosterone levels were higher after BC supplementation only in Bcmo1 ^−/− mice, which had, unlike wild-type (Bcmo1 ^+/+) mice, large variations. We hypothesize that BC possibly affects hormone synthesis or metabolism. Since sex hormones influence lung cancer risk, these data might contribute to an explanation for the previously found increased lung cancer risk after BC supplementation (ATBC and CARET studies). Moreover, effects of BC may depend on the presence of frequent human BCMO1 polymorphisms, since these effects were not found in wild-type mice.