Histone variants in plants. Evidence for primary structure variants differing in molecular weight

Variants of H2a and H2b histones from wheat embryos and pea shoots have been isolated and characterized by two-dimensional gel electrophoresis, amino acid content, and peptide mapping. In striking contrast to the animal H2a or H2b variants which co-migrate on sodium dodecyl sulfate polyacrylamide gels, their plant counterparts have differential electrophoretic mobilities. The estimated molecular weights of the wheat H2a variants range from 16,600 to 19,000. The H2b variants range from 15,300 to 19,000. Correlating with their electrophoretic mobilities, the plant histone variants elute differentially from gel exclusion columns in a manner consistent with the molecular weight differences inferred from the sodium dodecyl sulfate gels. The differences in peptide maps of the wheat H2a variants are extensive and indicate amino acid substitutions throughout the molecules. The maps of the plant H2a histones are also distinct from those of the major calf thymus H2a histones. The peptide maps of the plant H2b variants are very similar to each other but are markedly different from those of calf thymus H2b histones.