Chemical biology tools for studying histone post-translational modifications.

Post-translational modifications (PTMs) of histones are central regulators of chromatin organization and gene expression, providing a dynamic and reversible mechanism to encode cellular state. While advances in mass spectrometry have rapidly expanded the catalog of histone PTMs beyond classical acetylation and methylation, defining their functional roles remains a major challenge. A central bottleneck is linking specific PTMs to the enzymes that write and erase them, as well as the reader proteins that interpret them within native chromatin environments. The dysregulation of this regulatory machinery is increasingly implicated in cancer, neurodevelopmental disorders, and metabolic disease. Here, we argue that resolving PTM function requires integrating chemical precision with increasing biological complexity. We review chemical biology strategies for interrogating histone PTMs across this spectrum-from synthetic peptides to semisynthetic nucleosomes and intact chromatin-highlighting how each approach balances experimental control with physiological relevance and propose future directions for systematically mapping PTM-dependent interactions.