Expression array analysis

Quiescent (G_o) cultures of HCA2 cells were irradiated with 10 Gy and cultured for 1.5 h or 1 mo, and then total RNA was extracted with TRIzol (Ambion, Austin, TX). The Agilent Expression array (SurePrint G3), which screened relative levels of gene expression across the entire genome, was performed by Takara Co., Ltd. (Kyoto, Japan). By comparing the expression levels of the 0 Gy control, 10 Gy-1.5 h, and 10 Gy-1 Mo, genes with expression levels that were comparable, or reduced, at 10 Gy-1.5 h and then subsequently increased by more than twofold at 10 Gy-1 Mo were selected (Supplemental Data 1). Nuclear genes that were already known to be involved in chromatin regulation/nucleic acid metabolism were selected.