Histone H2A phosphorylation in animal cells: functional considerations.

We have sought to determine the role of histone H2A phosphorylation in chromatin by examining the distribution of the phosphorylated and unphosphorylated forms of this core histone within the nuclei of mouse and human cells. At any time, only about 15% of the H2A of whole chromatin is in the phosphorylated form, and its phosphate is rapidly turned over, even in quiescent cells that contain a functional nucleus. The phosphorylations and dephosphorylations are not specifically relate to progress through the cell cycle, nor to DNA synthesis or repair, and they are not selectively nucleolar. Euchromatin is substantially enriched with phosphorylated H2A but is not the exclusive repository of it. Possible roles of this modification of H2A are considered.