However, a significant increase in telomeric DNA within the soluble fraction was seen in A-T cells after one hour post treatment, whereas no such change in the release of matrix attached telomeric DNA was found in normal cells. An increase in the soluble fraction of the telomeric DNA in normal cells was seen only after one hour of treatment with doses above 10 Gy of ionizing radiation. We found relatively higher MNase digestion of chromatin in A-T cells as compared to normal cells. This suggests that nucleosomes in A-T cells are spaced loosely, thus leading to an altered periodicity. Since the ethidium bromide staining represents bulk chromatin, we were interested in examining nucleosomal patterns in telomere regions.
Normal cells have a telomere ladder, each containing partials up to seven subunits.
A different result is seen in A-T cells where the telomeric pattern revealed a less extensive MNase periodicity and telomeric nucleosomal arrays with up to three subunits were detected. These results suggest that the telomeric nucleosome arrays in A-T cells might be less uniformly spaced or might extend over a smaller region than the arrays. To determine how the altered nucleosomal periodicity in telomeres seen in A-T cells respond to ionizing radiations, we examined the influence of radiation treatment on nucleosomal compaction in telomeres. There was no change in the nucleosomal size of bulk chromatin as revealed by ethidium bromide staining. However we observed the disappearance of the mononucleosome band in the telomere region of A-T cells one hour after gamma ray treatment, whereas no such change was seen in normal cells.