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Reparability of lethal lesions produced by phosphorus photoabsorption in yeast cells

リンK殻X線吸収により酵母菌に生じる致死損傷の修復

宇佐美 徳子*; 横谷 明徳; 石坂 昭三*; 小林 克己*

Usami, Noriko*; Yokoya, Akinari; Ishizaka, Shozo*; Kobayashi, Katsumi*

リン原子のX線吸収により酵母細胞中に生じるDNA損傷の特性を、リンK殻のX線共鳴吸収波長(2153eV)及びこれよりも低エネルギー(2147eV)の単色化した放射光軟X線を用いて調べた。DNAの2重鎖切断(dsb)の相対修復率は、温度感受性dsb修復欠損突然変異株(${it rad 54-3}$)及び野生株を用いて測定した。${it rad 54-3}$に生じた損傷のうち修復された割合、すなわち${it RAD 54}$経路により修復され得るdsbの相対収率は、リンK殻X線共鳴吸収により影響を受けなかった。野生株に生じた損傷の修復に関しても、照射後ただちに培養した細胞と非栄養培地中で80時間保持した後に培養した細胞のそれぞれの生存率を比較することで調べた。液体保持回復処理を行った細胞の生存率の回復は、照射したX線のエネルギーに依存した。これらの結果は、リンの内殻X線吸収によりDNA中に修復され難い損傷が生じるが、その割合は小さいことを示してる。

The characteristics of DNA lesions produced by the phosphorus K-shell absorption in yeast cells were studied using monochromatized soft X-rays tuned to the phosphorus K-edge peak (2153 eV) and below the peak energy (2147 eV). The repaired fractions of DNA double-strand breaks (dsb) were measured relatively by using both a mutant, (${it rad 54-3}$), which shows the temperature-sensitive dsb repair-deficient, and a wild-type strain. The repaired fraction of lesion in ${it rad 54-3}$, which corresponds to the relative yield of dsb reparable by the ${it RAD 54}$ pathway, was not affected by the phosphorus photoabsorption. Repair of the produced lesions in the wild-type cells was also measured by comparing the surviving fraction of the immediately plated cells to that of those cells plated after holding in a non-nutrient medium for 80 hrs. The recovery of the surviving fraction after the holding treatment was dependent upon the soft X-ray energy. These results suggest that irrepairable lesions are produced by the inner-shell photoabsorption of phosphorus in DNA, although its yield is small.

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パーセンタイル:70.3

分野:Biology

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