Ubiquityl-Histone H3 (Lys18) (E4D7R) Rabbit mAb #37771

The nucleosome, made up of four core histone proteins (H2A, H2B, H3, and H4), is the primary building block of chromatin. Originally thought to function as a static scaffold for DNA packaging, histones have now been shown to be dynamic proteins, undergoing multiple types of post-translational modifications, including acetylation, phosphorylation, methylation, and ubiquitylation (1). Ubiquitin is a conserved 76 amino acid peptide unit that can be covalently linked to many cellular proteins by the ubiquitylation process. Three components are involved in this protein-ubiquitin conjugation process. Ubiquitin is first activated by forming a thiolester complex with the activation component E1; the activated ubiquitin is subsequently transferred to the ubiquitin-carrier protein E2, then from E2 to ubiquitin ligase E3 for final delivery to the epsilon-NH₂ of the target protein lysine residue (2). Histone H3 is mono-ubiquitinated at Lys14/Lys18/Lys23 by ubiquitin-like PHD and RING finger domain-containing protein 1 (UHRF1) and is deubiquitylated by ubiquitin-specific protease 7 (USP7) (3-5). UHRF1-mediated ubiquitylation of H3 at Lys14/Lys18/Lys23 (H3Ub) plays a critical role in maintaining DNA methylation states, as H3Ub recruits DNA methyltransferase 1 (DNMT1) to hemi-methylated DNA at replication sites during S phase (3). Conversely, deubiquitylation of H3 by USP7 is believed to abrogate DNMT1 docking to chromatin when replication is complete (4,5). Therefore, the interplay between UHRF1 and USP7 is believed to play a significant role in DNA methylation maintenance, and potential cancer therapies targeting USP7 are currently being investigated (6).