This animation shows how the protein MECP2 helps switch off gene expression.

A gene can be transcribed only when its surrounding chromatin is “open” and accessible to transcription factors, which requires nearby histone proteins to be acetylated (indicated with white balls in the animation). When upstream DNA is methylated (indicated with yellow spikes in the animation), MECP2 (methyl CpG binding protein 2) can bind to that DNA region. MECP2 recruits a protein complex that deacetylates the histones, causing the chromatin to condense and become inaccessible to transcription factors.

This animation is a clip from a 2003 Holiday Lecture Series, Learning From Patients: The Science of Medicine. Depending on students’ background, it may be helpful to pause the animation at various points to discuss different proteins or regions of DNA.