Nuclear histones in Physarum polycephalum during growth and differentiation

Abstract

The electrophoretic composition of the nuclear histones of Physarum polycephalum has been determined at various times during the mitotic cycle of the plasmodium and at all stages of the life cycle. During the mitotic cycle there were no marked changes in the relative amounts of the major histone components, but there were changes in a triplet of minor bands, with one band decreasing and another increasing during the period from early prophase to telophase. Histone:DNA ratios remained at about 1, on a weight basis, throughout the mitotic cycle but were slightly higher at the time of mitosis. Histone synthesis could occur when DNA synthesis was blocked by 5-fluorodeoxyuridine, and histone:DNA ratios could be increased to 3 by prolonged treatment with the drug. The nuclei of starving and sporulating plasmodia, and of spores, amoebae, and spherules all contained the seven histone bands characteristic of the growing plasmodia, but the relative amounts of the bands varied. The histone:DNA ratio was about 1 in amoebae and 0.8 in starving and sporulating plasmodia.