when CpG islands are unmethylated, DNAse hypersensitivity in that region of the chromosome is lost. chromatin in the enhancerSample Page region is closed, so they are unable to bind regulatory proteins to initiate transcription. genes downstream of the CpG islands cannot be expressed, because the promoter region is blocked by histones. chromatin in the promoter region is closed, preventing transcription factors and RNA polymerase from binding. Chromatin in the promoter region is open, allowing access by transcription factors and RNA polymerase.