DNA-degradation Products from Mammalian Cells Irradiated with Ultra-violet Light

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Abstract
Chinese hamster cells begin to die and degrade their DNA within 6 to 8 hours after 140 erg/mm2 and 700 erg/mm2 of u.v. light. Cell lysis releases macromolecular double-strand DNA and DNA degradative enzymes into the medium. Extracellular DNA degradation leads to an accumulation of thymidine and thymine in the medium. Intracellular degradation also occurs, and the acid-soluble fraction of the cells contains polynucleotides, phosphorylated derivatives of thymidine and thymine. Specific excision of thymine dimers in an acid-soluble form does not occur, and the contribution of DNA repair mechanisms to the observed degradation products is probably insignificant. No detectable amounts of DNA-degradation products (i.e. less than 0·05 per cent of total cellular DNA) were used for post-irradiation DNA synthesis.