An electrophoretic comparison of the histones of various strains of Tetrahymena pyriformis

Histones were extracted from isolated macronuclei of several strains of the ciliated protozoan Tetrahymena pyriformis and compared by electrophoresis on both urea-acrylamide and sodium dodecyl sulfate-acrylamide gels. High resolution urea-acrylamide-gel electrophoresis resolves Tetrahymena histones into five main classes. The lysine-rich histone H1 exhibits microheterogeneity within each strain, mostly due to phosphorylation, and varies extensively in electrophoretic mobility and apparent molecular weight among the strains. Both H3 and H4 are constant among Tetrahymena strains and consist of several secondarily modified subspecies. However, while the electrophoretic constancy of H4, observed in higher organisms, extends to this lower eukaryote, H3 of each Tetrahymena strain migrates faster than calf thymus H3 in both gel systems. This suggests that H3 is not as rigidly conserved as H4. Fraction HX has no electrophoretic counterpart in calf thymus histone. It consists of five subfractions, each of which displays a remarkably constant electrophoretic mobility among the various strains. H2B is electrophoretically variable among Tetrahymena strains. The intersyngen and interphenoset diversity of Tetrahymena histone is shown to be comparable to that found among vertebrate classes.