The study of epigenetic switches is very important to understand the mechanism of human development, the origin of cancer, mental illness and fundamental processes such as gene regulation. The bacteriophage epigenetic switch, which allows switching from lysogeny to lysis has recently received renewed attention. The interaction between the bacteriophage repressor and its DNA is an ideal model system to study DNA wrapping and looping and to reveal fundamental principles of long-range interactions and gene regulation by nucleoprotein complexes.