Abstract
Ionizing radiation causes DNA double strand breaks, which lead to change in the chromatin structure. Recently, it has been shown that altered chromatin structure induced by ionizing radiation induces autophosphorylation of ATM protein, by which dimeric or oligometric forms of ATM proteins are dissociated into monomeric form. Using antibodies against phosphorylated ATM at serine 1981, we examined how chromatin structure is changed after irradiation. Immediately after X-irradiation, we detected tiny foci of phosphorylated ATM, and the diameter was approximately 0.1 micrometer. The size of the foci was growing thereafter, and it reached approximately 1 micrometer 1 hour after irradiation. Growing the foci size was detected specifically in cells at G1 and G2 phase, and cells in S phase contained both tiny foci and growing foci. These results indicate that alteration in the chromatin structure is induced by DNA double strand breaks, but it is also suggested that chromatin remodeling is induced during DNA repair of double strand breaks.
