No abstract

When aqueous DNA solution was irradiated with 1.2 MHz continuous ultrasound in the presence of cysteamine, the number of ultrasound-induced double-strand breaks of DNA was not influenced, but the number of ultrasound-induced single-strand breaks of DNA was reduced to about one-fifth that of the irradiated control. When the effect of cysteamine on the template activity of the ultrasound-irradiated DNA was investigated, the cysteamine was found to exert a leveling effect on the linear decrease of the template activity against ultrasonic intensity. Since cysteamine was known as an effective radical scavenger, the results of the experiment were regarded to suggest that (1) the double-strand breaks were exclusively induced by the mechanical effect of ultrasound, (2) the majority of single-strand breaks were produced by water radicals arising from cavitation, (3) the initial part in the decrease of the template activity was due to the double-strand breaks arising from mechanical effect, and (4) the further decrease of the template activity depended mainly on the single-strand breaks arising from water radicals.

ABSTRACT. The effect of X-irradiation of cell lines from LEC and WKAH strain rats on a progression of cell cycle was investigated. When WKAH rat cells were exposed to 5 Gy of X-rays and their cell cycle distribution was determined by a flow cytometer, the proportion of Sphase cells decreased and that of G2/M-phase cells increased at 8 hr post-irradiation. At 18 and 24 hr post-irradiation, approximately 80% of the cells appeared in the G1 phase. On the contrary, the proportion of S-phase cells increased and that of G1-phase cells decreased in LEC rats during 8-24 hr post-irradiation, compared with that at 0 hr post-irradiation. Thus, radiation-induced delay in the progression from the G1 phase to S phase (G1 arrest) was observed in WKAH rat cells but not in LEC rat cells. In the case of WKAH rat cells, the intensities of the bands of p53 protein increased at 1 and 2 hr after X-irradiation at 5 Gy, compared with those of unirradiated cells and at 0 hr post-irradiation. In contrast, the intensities of the bands were faint and did not significantly increase in LEC rat cells during 0-6 hr incubation after X-irradiation. Present results suggested that the radioresistant DNA synthesis in LEC rat cells is thought to be due to the abnormal G1 arrest following X-irradiation. -KEY WORDS: cell cycle, G1 arrest, LEC strain rat, p53 protein, X-irradiation.J. Vet. Med. Sci. 59(9): 769-773, 1997 to S phase in the cell lines derived from lung fibroblasts of LEC rats and showed an abnormal G1 arrest following Xirradiation. MATERIALS AND METHODS Culture of the cells and X-irradiation:The rat fibroblast cell lines were established from lungs of LEC and WKAH rats by SV 40 immortalization as described previously [7]. Cells were grown in monolayer culture in Eagle's minimum essential medium (MEM) containing 10% fetal calf serum (FCS). Cell cultures were kept at ambient humidity and 37°C in an atmosphere containing 5% CO 2 .X-irradiation was carried out utilizing a Hitachi MBR-1520R X-ray generator operated at 150 kV and 15 mA with a 0.5 mm Cu + 1.0 mm Al filter at a dose rate of 0.95 Gy/ min.Flow cytometry: The cell cycle phase distribution of a cell population was determined by measuring the DNA content of individual cells by flow cytometry. In preparation for flow cytometry, cells (1 × 10 6 to 5 × 10 6 ) were exposed to 5 Gy of X-rays. After X-irradiation, the cells were incubated at 37°C for 0-24 hr, harvested by trypsinization, washed with PBS and then pelleted by centrifugation at 500 × g. The cells were fixed in 5 ml of cold 70% ethanol for 30 min at room temperature and then stored at 20°C. Just prior to flow cytometric analysis, individual samples were treated with RNase (1 mg/ml) for 30 min at room temperature and then stained with propidium iodide according to the manufacturer's instructions for the cellular DNA flow cytometric analysis reagent set (Boeringer Mannheim). Fluorescence was measured with a Coulter EPICS Elite flow sorter using a 610-nm filter. Cell cycle distribution was determined using multicycle software. ...

Glycolate (GL)-containing polyhydroxyalkanoate (PHA) was synthesized in Escherichia coli expressing the engineered chimeric PHA synthase PhaCAR and coenzyme A transferase. The cells produced poly[GL-co-3-hydroxybutyrate (3HB)] with the supplementation of GL and 3HB, thus demonstrating that PhaCAR is the first known class I PHA synthase that is capable of incorporating GL units. The triad sequence analysis using 1H nuclear magnetic resonance indicated that the obtained polymer was composed of two distinct regions, a P(GL-ran-3HB) random segment and P(3HB) homopolymer segment. The random segment was estimated to contain a 71 mol% GL molar ratio, which was much greater than the value (15 mol%) previously achieved by using PhaC1PsSTQK. Differential scanning calorimetry analysis of the polymer films supported the presence of random copolymer and homopolymer phases. The solvent fractionation of the polymer indicated the presence of a covalent linkage between these segments. Therefore, it was concluded that PhaCAR synthesized a novel random-homo block copolymer, P(GL-ran-3HB)-b-P(3HB).