Histone H2Ais one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells. Histones are proteins that package DNA into nucleosomes. Histones are responsible for maintaining the shape and structure of a nucleosome. One chromatin molecule is composed of at least one of each core histones per 100 base pairs of DNA. There are five families of histones known to date; these histones are termed H1/H5, H2A, H2B, H3, and H4. H2A is important for packaging DNA into chromatin. Since H2A packages DNA molecules into chromatin, the packaging process will effect gene expression.H2A has been correlated with DNA modification and epigenetics. H2A plays a major role in determining the overall structure of chromatin. Inadvertently, H2A has been found to regulate gene expression. DNA modification by H2A occurs in the cell nucleus. The proteins responsible for nuclear import of H2A protein are karyopherin and importin. Recent studies also show that nucleosome assembly protein 1 is also used to transport of H2A into the nucleus so it can wrap DNA.