A reduction in the degree of H4 acetylation during mitosis in Chinese hamster cells

Long polyacrylamide gels and curve-resolving methods were used to separate and quantitate histone H4 acetylated subfractions from synchronized line CHO Chinese hamster cells. The proportion of internally acetylated H4 molecules was found to be highest during interphase. A reduction in the proportion of acetylated H4 occurred as cells entered mitosis, and a minimum was measured during prophase and metaphase, the periods of maximal chromosomal condensation. A rapid increase in the proportion of acetylated H4 was observed as chromosomes became dispersed in telophase. These observations in proliferating cells are in accord with prior observations in differentiating systems and support the concept that H4 acetylation is minimal when chromatin is highly condensed and RNA synthesis is minimal.