HISTONES OF GENETICALLY ACTIVE AND INACTIVE CHROMATIN

It has frequently been proposed that a variation in the relative content of lysine-rich, moderately lysine-rich, and arginine-rich histones might provide a mechanism by which specific portions of the genome may be genetically regulated. This possibility was investigated by comparing the electrophoretic pattern of these three fractions in cells differing markedly in their content of genetically active and genetically inactive chromatin. Three models were used: heterochromatin versus euchromatin; metaphase cells versus interphase cells, and mature lymphocytes versus phytohemagglutinin-stimulated lymphocytes. In no case was there a significant difference in the histone patterns of these contrasting models. It is concluded that, although histones may act as a generalized repressor and structural component of chromatin, factors other than a variation in histone pattern may be responsible for repression or derepression of specific segments of the genome.