Light-induced conformational change and product release in DNA repair by (6-4) photolyase

Proteins of the cryptochrome/photolyase family share high sequence similarities, common folds, and the flavin adenine dinucleotide (FAD) cofactor, but exhibit diverse physiological functions. Mammalian cryptochromes are essential regulatory components of the 24 h circadian clock, whereas (6-4) photolyases recognize and repair UV-induced DNA damage by using light energy absorbed by FAD. Despite increasing knowledge about physiological functions from genetic analyses, the molecular mechanisms and conformational dynamics involved in clock signaling and DNA repair remain poorly understood. The (6-4) photolyase, which has strikingly high similarity to human clock cryptochromes, is a prototypic biological system to study conformational dynamics of cryptochrome/photolyase family proteins. The entire light-dependent DNA repair process for (6-4) photolyase can be reproduced in a simple in vitro system. To decipher pivotal reactions of the common FAD cofactor, we accomplished time-resolved measurements of radical formation, diffusion, and protein conformational changes during light-dependent repair by full-length (6-4) photolyase on DNA carrying a single UV-induced damage. The (6-4) photolyase by itself showed significant volume changes after blue-light activation, indicating protein conformational changes distant from the flavin cofactor. A drastic diffusion change was observed only in the presence of both (6-4) photolyase and damaged DNA, and not for (6-4) photolyase alone or with undamaged DNA. Thus, we propose that this diffusion change reflects the rapid (50 μs time constant) dissociation of the protein from the repaired DNA product. Conformational changes with such fast turnover would likely enable DNA repair photolyases to access the entire genome in cells.     

Reaction of O6-methylguanosine with nitrite in the presence of carboxylic acid: synthesis of the purin-2-yl carboxylate

O6-Methylguanosine derivative was treated with sodium nitrite or isoamylnitrite in the presence of carboxylic acid to give the purin-2-yl carboxylate, an unusual product bearing a carboxylic group at the 2-position of the purine moiety.     

Kaon condensation and lambda–nucleon loop in the relativistic mean-field approach

The possibility of kaon condensation in high-density symmetric nuclear matter is investigated including both s- and p-wave kaon–baryon interactions within the relativistic mean-field (RMF) theory. Above a certain density, we have a collective state carrying the same quantum numbers as the antikaon. The appearance of the state is caused by the time component of the axial-vector interaction between kaons and baryons. It is shown that the system becomes unstable with respect to condensation of K– pairs. We consider how the effective baryon masses affect the kaon self-energy coming from the time component of the axial-vector interaction. Also, the role of the spatial component of the axial-vector interaction on the possible existence of the collective kaonic states is discussed in connection with Λ-mixing effects in the ground state of high-density matter. Implications of condensation for high-energy heavy-ion collisions are briefly mentioned.     

Elastic electron deuteron scattering

Measurements of the ratio of the deuteron to proton electric form factors were made for low q. The rms radius of the deuteron structure factor was found to be 1.9635 ± 0.0045 fm, yielding an rms charge radius of 2.095 ± 0.006 fm.     

Elongation of carbonyl compounds by utilizing electroreduction as a key step

The transformation of aldehydes, ketones and esters to the next higher homologous aldehydes was accomplished by utilizing electroreductive 1,2-elimination as a key step.     

The oldest mid-oceanic carbonate buildup complex: Setting and lithofacies of the Vendian (Late Neoproterozoic) Baratal limestone in the Gorny Altai Mountains,Siberia

The Baratal limestone in the Gorny Altai Mountains, southern Siberia, occurs as large allochthonous blocks within a Cambrian accretionary complex that developed around the Siberia craton. Before the final accretion to Siberia in the Cambrian, the terrigenous clastic-free Baratal limestone was deposited directly upon a basaltic basement with a geochemical signature identical to that of modern oceanic plateau. The Baratal limestone with 598 ± 25 Ma (Early Vendian) Pb-Pb isochron age consists of three distinct facies; 1) massive lime mudstone with ooids and stromatolites, 2) bedded lime mudstone, and 3) limestone conglomerate/breccia dominated by ooid-bearing lime mudstone clasts. The first represents a shallow marine environment on top of an ancient oceanic plateau, while the latter two represent the deeper slope to bottom-of-slope facies of a plateau. The Vendian Baratal limestone provides the oldest example of a reconstructed shallow marine carbonate buildup complex developed on a plateau/seamount in a mid-ocean.     

Synthesis and characterization of poly[4-(4-hydroxyphenoxy) benzoic acid]

Poly[4-(4-hydroxyphenoxy) benzoic acid] was prepared by the bulk polycondensation of 4-(4-acetoxyphenoxy) benzoic acid. Polycondensation was conducted at 350°C for 3 h under a reduced pressure of 0.1 mmHg and gave a polymer with X?n of 255. The polymer was characterized by elemental analysis, IR spectroscopy, differential scanning calorimetry, and wide-angle X-ray measurement. The crystal/nematic and nematic/isotropic phase transition temperatures of polymer, which depend on the molecular weight, were observed at about 300°C and 410°C, respectively. The polymers with low molecular weights showed nematic textures above 300°C. This nematic/isotropic phase transition temperature is lower than that of poly (4-hydroxybenzoic acid). This thermal behavior of polymer comes from ether units, which increase the flexibility (the rotation or torsion of skeletal bonds) of the polymer chain. © 1994 John Wiley & Sons, Inc.     

Stereospecific synthesis of chiral precursors of thienamycin from L-Threonine

L-Threonine was transformed, stereospecifically, to a versatile β-lactam (5a) in 3 steps. This β-lactam was further converted to a key intermediate (25) for the synthesis of thienamycin and its biologically active analogues. Furthermore, the compound 5a was changed to iodides (18 and 23), cyanides (19 and 24), chloromethylketone (26) and aldehydes (30 and 31) which appear to have a latent potential as precursors for the syntheses of the carbapenems.