| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1988: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1987: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1986: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
I have been studying the role of conformational changes of DNA-chromatin in the expression potentially lethal damage(PLD), using temperature-sensitive mutants(ts-mutants) derived from baby hamster kidney cells(BHK21). Main results obtained thus far are as follows: 1) In the tsBN2 cell line, which has a ts-defect in the regulatory mechanism for the onset of chromosome condensation and in which premature chromosome condensation(PCC) occurs irrespective of the cell cycle at the nonpermissive temperature(40゜C), the lethal effect of X-rays was enhanced by incubating the cells at 40゜C following X-irradiation. 2) PCC was induced by caffeine in the presence of DNA-synthesis inhibitor in eight ts-mutants at the permissive temperature(33.5゜C), but its induction was suppressed by the incubation at 40゜C in three ts-mutants(BN75,BN250,BTN1). 3) PLD was expressed markedly by inducing PCC in the presence of caffeine and DNA-synthesis inhibitor following X-irradiation. However, the expression of pld with caffeine alone could not be suppressed by protein-synthesis inhibitor, which inhibits PCC-induction, indicating no involvement of PCC. 4) Expression of PLD with caffeine alone was suppressed by preincubation at 40゜C in BN75 cell line, which has a ts-defect in ubiquitin-activating enzyme.
These results suggest the following model on the mechanisms of PLD expression by nonpermissive temperature(BN2) and caffeine. In BN2 cell line, repressor(RCC1) for trigger protein, which induces chromosome condensation, is temperature-sensitive, and PCC is induced at the nonpermissive temperature. Caffeine triggers the ubiquitin-system and degradates RCC1 in the presence of DNA-synthesis inhibitor, thus inducing PCC. Caffeine alone also induces the conformational changes of DNA-chromatin by degradating histanes via another pathway of the ubiquitin-system. All these changes induced post X-irradiation will be favorable for the expression of PLD.
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