Scientists have discovered a new type of chemical decoration on lysine groups of histone proteins—around which DNA in a nucleus is wound—that helps differentiate male germ cells into sperm. That’s just one confirmed role for lysine 2-hydroxyisobutyrylation (Khib), which was identified by a team led by Saadi Khochbin of Joseph Fourier University, in France, and Yingming Zhao of the University of Chicago (Nat. Chem. Biol. 2014, DOI: 10.1038/nchembio.1497). The researchers found that 63 lysine sites on mouse and human histone proteins feature the lysine 2-hydroxyisobutyrylation epigenetic mark—a greater number of modifications than the more commonly known lysine acetylation posttranslational mark. The team points out that this new mark contributes more physical bulk to lysine groups than methylation or acetylation. It also features a hydroxyl group capable of forming hydrogen bonds with other molecules in the nucleus. Although the team focused on studying the epigenetic marks involved in sperm production, they have evidence that the new lysine modification is also found in other tissues and likely controls additional biological functions.