The Effect of Phytohemagglutinin on Ribonucleic Acid Synthesis and Histone Acetylation in Equine Leukocytes

It is well known that peripheral lymphocytes rarely divide in tissue culture; indeed, they have usually been considered to be the end cell in the pathway of differentiation. However, in the presence of certain mitogenic agents, of which phytohemagglutinin (PHA) is the best known example, a striking transformation occurs; the cells increase their over-all metabolic activity, enlarge, and divide. This response of the small lymphocyte, widely studied since its discovery in 1960 (1, 2), is now known to involve an increased synthesis of ribonucleic acids (3-5). It has also been observed that histone metabolism is altered very early in the process of gene activation for RNA synthesis (5). The acetylation of arginine-rich histones, in particular,