by labelling the cytosine moieties of these repair patches , and measuring the ratio between cytosine and 5-methylcytosine , we have found that the level of methylation of cytosine in repair patches five hours after uv-irradiation of the cells is about half of that observed in normal semiconservatively synthesized dna .
C0010843
cytosine
C0049308
5-methylcytosine