H2B

H2B refers to histone H2B, a core protein of chromatin in eukaryotic cells. Along with histones H2A, H3, and H4, H2B participates in forming the histone octamer around which about 146 base pairs of DNA are wrapped to create a nucleosome, the fundamental unit of chromatin. In most organisms, H2B proteins pair with H2A to form H2A-H2B dimers that associate with the H3-H4 tetramer to assemble the nucleosome core particle.

The HIST1 and related gene clusters encode replication-dependent histone H2B variants. These genes are typically intronless and are expressed mainly during S-phase to supply histones for DNA packaging during replication. There are also replication-independent H2B variants that are expressed in differentiated or specialized cell types, contributing to chromatin diversity in different contexts.

H2B carries conserved N-terminal tails that are subject to various post-translational modifications, including acetylation, methylation, phosphorylation, and ubiquitination. One well-studied modification is monoubiquitination of H2B at lysine 120 (H2Bub1), which is linked to transcriptional elongation and the DNA damage response in many species. Other modifications commonly correlate with transcriptional activity and chromatin state.

Beyond DNA packaging, H2B participates in chromatin remodeling and gene regulation, replication, and repair. It interacts with histone chaperones such as FACT and Asf1, which assist in depositing and removing H2A-H2B dimers during nucleosome assembly and disassembly. As a highly conserved protein, H2B variants contribute to chromatin dynamics and genome regulation across eukaryotes.