Youichi Fujii

The mouse Rad51 gene is a mammalian homologue of the Escherichia coli recA and yeast RAD51 genes, both of which are involved in homologous recombination and DNA repair. To elucidate the physiological role of RAD51 protein, the gene was targeted in embryonic stem (ES) cells. Mice heterozygous for the Rad51 null mutation were intercrossed and their offspring were genotyped. There were no homozygous (Rad51-/-) pups among 148 neonates examined but a few Rad51-/- embryos were identified when examined during the early stages of embryonic development. Doubly knocked-out ES cells were not detected under conditions of selective growth. These results are interpreted to mean that RAD51 protein plays an essential role in the proliferation of cell. The homozygous Rad51 null mutation can be categorized in cell-autonomous defects. Pre-implantational lethal mutations that disrupt basic molecular functions will thus interfere with cell viability.

A fifteen year investigation of marine animal components as sources for new and potentially useful cancer chemotherapeutic drugs has led to our discovery of a number of such valuable substance. The especially productive Indian Ocean sea hare Dolabella auricularia has yielded (100 kg leads to or approximately 1 mg each) a series of very potent cell growth inhibitory substances designated dolastatins 1-9. The first member of this new series, dolastatin 1, may represent the most potent anticancer agent so far uncovered with, e.g., a curative response (33%) using a dose of 11 microgram/kg (T/C 240, to T/C 139 at 1.37 microgram/kg) in the National Cancer Institute's murine B16 melanoma. Structural elucidation of the new antineoplastic agents is underway, and recent progress is illustrated with peptide dolastatin 3 (P388 ED 50 2.7 x 10(-7) microgram/ml).

Abstract A selective determination method for mercury(II) ion in water by reversed‐phase high performance liquid chromatography (HPLC) has been developed. A water sample of 5 mL was put into a 10‐mL centrifuge tube with a stopper. Then, 1 mL of 2‐mol/L (M) acetate buffer solution of pH 5.5 was added into the centrifuge tube. After mixing the contents, 1 mL of 0.5 M tetrabutylammonium bromide (TBA‐Br) solution and 0.3 mL of 1‐octanol were added. A mercury ion was extracted into an organic layer by shaking the contents for 10 min. The organic layer of 8 µL was injected into a C18 column with an eluent of methanol/water/0.5 M TBA‐Br (65:31:4, v/v), and the effluent was monitored at 255 nm. The detected mercury compound was estimated as [(TBA+)2 · HgBr4 2−]0. The correlation coefficient of the calibration curves (metal concentration vs. peak area), obtained with 5 mL of mercury standard, was more than 0.999 over the range of 10 ng/mL (ppb) to 10 µg/mL (ppm). The detection limit of Hg ion in a 5‐mL solution was 0.8 ppb, which corresponded to three times the standard deviation of the blank peak area. Reproducibilities (RSD) of peak areas for 5‐, 0.5‐, and 0.05‐ppm Hg ion were 1.8%, 0.6%, and 0.6%, respectively (N = 5). Recovery tests were carried out by the presented HPLC method with spiked river water samples. The recoveries for 5‐, 0.5‐, and 0.05‐ppm Hg ion were 99.5%, 102.9%, and 99.8%, respectively. Effects of foreign ions on the method were investigated with 0.2‐ppm Hg standard and 55 metal ions. Tolerance limits of Be(II) and Sc(III) were 20 ppm, and those of Bi(III) and Pd(II) were 40 ppm. The other metal ions of 100 ppm, or more, did not interfere with the determination of mercury(II) ion.

<p>A roll-to-roll high-current diffuse dielectric barrier discharge at atmospheric pressure was operated in air and Ar/N<sub>2</sub>/O<sub>2</sub> gas mixtures. The exhaust gas from the discharge was studied using a high-resolution Fourier-transform infrared spectrometer in the range from 3000 to 750 cm<sup>-1</sup> to unravel the plasma-polymer interactions. The absorption features of H<sub>x</sub>N<sub>y</sub>O<sub>z</sub>, CO<sub>x</sub>, and HCOOH (formic acid) were identified, and the relative densities were deduced by fitting the absorption bands of the detected molecules. Strong interactions between plasma and polymer (Polyethylene-2,6-naphthalate, or PEN) in precursor-free oxygen-containing gas mixtures were observed as evidenced by a high CO<sub>x</sub> production. The presence of HCOOH in the gas effluent, formed through plasma-chemical synthesis of CO<sub>x</sub>, turns out to be a sensitive indicator for etching. By adding tetraethylorthosilicate precursor in the plasma, dramatic changes in the CO<sub>x</sub> production were measured, and two distinct deposition regimes were identified. At high precursor flows, a good agreement with the precursor combustion and the CO<sub>x</sub> production was observed, whereas at low precursor flows an etching-deposition regime transpires, and the CO<sub>x</sub> production is dominated by polymer etching.</p>