H3S28P is an epigenetic modification to the DNA packaging protein histone H3. It is a mark that indicates the phosphorylation the 28th serine residue of the histone H3 protein. Early mitosis phosphorylation patterns for H3S10 and H3S28 are quite similar, starting at the initiation of chromosomal condensation during prophase. At gene promoters, H3S28 phosphorylation is expected to remove Polycomb restrictive complexes from chromatin, causing demethylation and acetylation of the nearby K27 residue, so activating transcription. This transition is mediated by the phosphorylation of H3S28 on a site next to H3K27. It was discovered that phosphorylating H3S28 in the promoters of genes like c-fos and -globin controlled their activation.