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. High expression in root meristematic tissues, moderate in whole shoot and very low in mature leaves. Expressed during the late G1 phase and the major part of the S phase. Contains 2 SPKK motifs which may interact with the minor groove of A/T-rich DNA sites. Phosphorylation of this motif may regulate DNA binding. This motif is reiterated in both termini of histone H1 and in the N-terminus of sea urchin histones H2B, but its presence in the C-terminus seems to be unique to plant H2A. Belongs to the histone H2A family.