Figure 4.

A schematic representation showing distinguishing features between repressive and permissive DNA methylation. (a) Repressive methylation peaks are on average 893±110 bp upstream of the transcription start site of target genes, which are characterized by a relatively lower maximum CpG island density. Chromatin is closed at the transcription start site as indicated by the absence of DNase I HS sites. (b) Permissive methylation peaks are further upstream from transcription start site compared with repressive peaks, and are characterized by higher maximum CpG island densities within promoter sequences of target genes. These methylation peaks fail to maintain a closed chromatin configuration. This results in accessible chromatin at the transcription start sites of target genes as evidenced by the presence of DNase I HS sites and gene expression. It is possible that these methylation peaks fail to efficiently recruit transcriptional repressor complexes, such as the MECP2–SIN3A–HDAC complex. MECP2, methyl-CpG-binding protein 2; SIN3A, SIN3 homolog A; HDAC, histone deacetylase.