Degrees make all the difference: the multifunctionality of histone H4 lysine 20 methylation.

Residue and degree-specific methylation of histone lysines along with other epigenetic modifications organizes chromatin into distinct domains and regulates almost every aspect of DNA metabolism. Identification of histone methyltransferases and demethylases, as well as proteins that recognize methylated lysines, has clarified the role of each methylation event in regulating different biological pathways. Methylation of histone H4 lysine 20 (H4K20me) plays critical roles in diverse cellular processes such as gene expression, cell cycle progression and DNA damage repair, with each of the three degrees of methylation (mono-, di- and tri-methylation) making a unique contribution. Here we discuss recent studies of H4K20me that have greatly improved our understanding of the regulation and function of this fascinating histone modification.