Phosphorylation of Plant H2A Histones

Abstract

Phosphorylation of wheat (Triticum aestivum) and alfalfa (Medicago sativa) H2A histone variants was examined during early seedling growth. The C-terminal regions of wheat H2A variants contain multiple S-P tetrapeptides (serine-proline adjacent to a pair of basic amino acids) which resemble known phosphorylation sites in histones from other species. Phosphorylation of nucleosomal core histones was assessed by autoradiography of proteins labeled in vivo with ³²Pi and resolved by two-dimensional polyacrylamide gel electrophoresis, and phosphorylation sites were mapped by cleaving in vivo labeled H2A variants with N-bromosuccinimide. Essentially all phosphorylation of nucleosomal core histones in wheat and alfalfa seedlings occurred within the C-terminal peptides obtained from wheat and alfalfa H2A variants. A hypothesis accounting for the presence of large H2A and H2B histone variants in plants and phosphorylation of plant H2A C-terminal regions is proposed. The utility of S-P tetrapeptides for modulation of DNA-protein interactions is discussed.