Rearrangements of chromatin structure in newly repaired regions of deoxyribonucleic acid in human cells treated with sodium butyrate or hydroxyurea

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Abstract
The rate and extent of redistribution of repair-incorporated nucleotides within chromatin during very early times (10-45 min) after UV irradiation were examined in normal human fibroblasts treated with 20 mM sodium butyrate, or 2-10 mM hydroxyurea, and compared to results for untreated cells. Under these conditions, DNA replicative synthesis is reduced to very low levels in each case. DNA repair synthesis is stimulated by sodium butyrate and partially inhibited by hydroxyurea. In the sodium butyrate treated cells, the core histones are maximally hyperacetylated. Treatment with sodium butyrate had little or no effect on either the rate or the extent of redistribution of repair-incorporated nucleotides during this early time interval. There was a 1.7- to 2.5-fold decrease in the rate of redistribution of these nucleotides in cells treated with hydroxyurea; the extent of redistribution was unchanged in these cells. Since hydroxyurea was shown to decrease the rate of completion of repair patches in mammalian cells, these results indicate that nucleosome rearrangement in newly repaired regions of DNA does not occur until after the final stages of the excision repair process are completed. Hyperacetylation of the core histones in a large fraction of the total chromatin prior to DNA damage and repair synthesis does not appear to alter the rate or extent of nucleosome core formation in newly repaired regions of DNA.

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