Multiplicity of histone h3 variants in wheat, barley, rice, and maize.

Histone H3 proteins were purified to near homogeneity from etiolated seedlings of wheat (Triticum aestivum), barley (Hordeum vulgare), rice (Oryza sativa), maize (Zea mays), and alfalfa (Medicago sativa) to determine the number of histone H3 variants. Five distinct histone H3 variants were identified by gradient gel electrophoresis and reversed phase chromatography. These variants occur in various combinations of two to four forms in each plant species. One minor histone variant form (variant III, named H3.2 in alfalfa) appeared present and identical in all mono- and dicotyledonous plant species tested to date. All H3 proteins were acetylated to multiple levels and in every species the variant III form was acetylated most extensively. The level of histone H3 acetylation showed an inverse correlation with plant genome size. These observations support the idea that acetylated histones and especially variant III proteins are an element of transcriptionally active chromatin.