(a) CpG islands of the mouse p53 gene from exon 4 to exon 9. Underlined sequences indicate CpG islands that were searched using Methyl Primer Express Software v1.0. The cytosine (C) surrounded by a rectangle is the CpG site. (b) The sequence of the CpG islands after bisulfite conversion. The boxed area indicates the forward and reverse primer sets. Underline sequences refer to exons 5 and 6. (c) Electropherograms of PCR products after subcloned plasmid DNA in 8-week-old and 122-week-old p53^+/+ mice. In 8-week-old mice, a “C” was converted to a “T”. In 122-week-old mice, a “C” was retained as a “C”.