Schematic representation of the interaction between promoter methylation and transcription of the gene. In the absence of DNA methylation, TFs can bind DNA allowing RNA polymerase to bind and to start the transcription. Panel a shows the following scenario: if DNA becomes methylated, TFs are blocked from binding to DNA and therefore RNA polymerase is unable to bind and to initiate transcription. Panel b shows the following scenario: chromatin modifications reduce the ability of TFs to bind DNA and therefore RNA polymerase is unable to bind; the repressed condition of the chromatin is maintained by subsequent DNA methylation. PolII is shown as a maroon pie; nucleosome is shown as a blue cylinder. Plain (solid) lollipops represent unmethylated (methylated) cytosines. TF is shown as an orange octagon. The green hexagon and purple trapezoid are a methyl-binding domain and Policomb-group proteins, respectively. The brown triangle represents an unknown repressor.