To manage the 30-40 000 genes in the human genome, nature has evolved a sophisticated system, based around chromatin, which facilitates their access. Fully understanding the way chromatin gets tweaked by enzymes will be crucial to the development of anti-cancer therapeutics, for example, HDAC inhibitors (HDACI). David and his team favour the view that there is an epigenetic indexing system, a 'histone code' that acts outside of the DNA itself. He believes that the 'code' affects all processes related to chromatin, influencing cell fate but also diseases of the whole organism.