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. Required for the T-DNA integration step of plant transformation by Agrobacterium. May play an important role in illegitimate recombination. 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. Interacts with VIP1. Low level of expression, mainly in dividing tissues: floral buds, margins of newly emerging leaves, expanding leaves and the meristematic zone of root tips. Also expressed in many non-dividing cells of the elongation zone of the root. By phytohormones. Transiently by wounding. Not ubiquitinated. RAT5 is required for Agrobacterium-mediated transformation of root but not of germ-lime tissues. Belongs to the histone H2A family.