Core component of nucleosome. Nucleosomes wrap and compact DNA into chromatin, limiting DNA accessibility to the cellular machineries which require DNA as a template. Histones thereby play a central role in transcription regulation, DNA repair, DNA replication and chromosomal stability. DNA accessibility is regulated via a complex set of post-translational modifications of histones, also called histone code, and nucleosome remodeling. The nucleosome is a histone octamer containing two molecules each of H2A, H2B, H3 and H4 assembled in one H3-H4 heterotetramer and two H2A-H2B heterodimers. The octamer wraps approximately 147 bp of DNA. Can be acetylated to form H2BK6ac and H2BK33ac. Monoubiquitinated by BRE1 to form H2BK143ub1 and deubiquitinated by UBP26. Required for heterochromatic histone H3 di- and trimethylation at H3K4me. May give a specific tag for epigenetic transcriptional activation (By similarity). Belongs to the histone H2B family. To ensure consistency between histone entries, we follow the 'Brno' nomenclature for histone modifications, with positions referring to those used in the literature for the 'closest' model organism. Due to slight variations in histone sequences between organisms and to the presence of initiator methionine in UniProtKB/Swiss-Prot sequences, the actual positions of modified amino acids in the sequence generally differ. In this entry the following conventions are used: H2BK6ac = acetylated Lys-7; H2BK33ac = acetylated Lys-35; H2BK143ub1 = monoubiquitinated Lys-148.