Histones serve as slates to a dizzying array of modifications, but researchers are confident they can decipher the epigenetic puzzle.

Roughly two meters of DNA gets packed into every cell nucleus in the human body. In addition to stuffing all that information into a sphere 3 to 10 microns across, the proteins that perform this task must also ensure that in each cell certain genes are constantly transcribed, while others lie ready, and other regions remain dormant, practically inaccessible. Within this cramped, chaotic space, an army of proteins must manage cellular information, decide cell fate with a moment's notice and maintain it, often passing that fate to daughter cells.

This regulation takes place in the context of the histone proteins. Two each of the four standard histones - H3, H4, H2A, and H2B - join together to form an...