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. Has broad-spectrum antimicrobial and antibacterial activity. It is important in the antimicrobial defenses of fish skin and possesses strong activity against saprolegnia, the most common fungal infection in fish. It is also inhibitory to fish bacterial pathogens, such as aeromonas hydrophila, vibrio alginolyticus and E.coli D31. 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. Monoubiquitination at the C-terminal Lys gives a specific tag for epigenetic transcriptional activation and is also prerequisite for histone H3 'Lys-4' and 'Lys-79' methylation. Phosphorylated during apoptosis; which facilitates apoptotic chromatin condensation. The measured range is 2-21. Belongs to the histone H2B family.