Figure 1.
Overall strategy for cloning methylated CpG islands. In step 1, genomic DNA was digested with Mse I (red), which cuts between CpG islands, and Hpa II (blue), which cuts unmethylated CpG islands. Mse I fragments containing methylated CpG islands then are transformed into a bacterial strain that does not cut methylated DNA. However, brief bacterial passage leads to loss of methylation of these previously methylated sequences. In step 2, the library DNA is pooled and digested with Eag I (green), which cuts relatively large fragments within CpG islands, and these fragments are then subcloned.
