A Study on the Mechanism of Photoreactivation in <i>Escherichia coli</i>

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  • 大腸菌における紫外線障害の光修復機構に関する研究
  • ダイチョウキン ニ オケル シガイセン ショウガイ ノ ヒカリ シュウフク キコウ ニ カンスル ケンキュウ

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Photoreactivation of ultraviolet (UV) damage has been demonstrated in many bacteria, plants and animals.<br>In the previous paper, we reported on the phenomenon of photoreactivation in vitamin B1 requiring mutants of E. coli B. The present study was performed to clarify the mechanism of photoreactivation.<br>E. coli DNA labeled with 3H-thymidine was irradiated with UV light of 255mμ. In the presence of visible light, the irradiated DNA was incubated with enzyme which was extracted from E. coli B. The reaction was terminated by addition of trichloroacetic acid. The precipitated DNA was hydrolyzed with formic acid, paper chromatographed and the radioactivity of each fraction was counted.<br>As the result of this experiment, a new radioactive peak of thymine dimer with Rf value 0.24 was observed.<br>However, about 30% of the dimers were split off from irradiated DNA by photoreactivating treatment.<br>It was concluded that photoreactivating enzyme exists in E. coli B, and UV-induced thymine dimers in DNA are eliminated by the enzyme in the presence of light.

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