High levels of acetylation of lysines in the amino-terminal domains of all four core histones, H2A, H2B, H3, and H4, have been shown to reduce the linking number change per nucleosome core particle in reconstituted minichromosomes (Norton, V. G., Imai, B. S., Yau, P., and Bradbury, E. M. (1989) Cell 57, 449-457). Because there is evidence to suggest that the acetylations of H3 and H4 have functions that are distinct from those of H2A and H2B, we have determined the nucleosome core particle linking number change in minichromosomes containing fully acetylated H3 and H4 and very low levels of acetylation in H2A and H2B. This linking number change was -0.81 +/- 0.05, in close agreement with the linking number change for hyperacetylated nucleosome core particles which contain high levels of acetylation in all four core histones (approximately 70% of full acetylation in H3 and H4). Therefore, high levels of acetylation of H3 and H4 alone are responsible for the reduction in the linking number change per nucleosome core particle.