The semihistone protein, A24, was shown to be a stable minor component of purified salt-washed nucleosome core particles. A24 was also shown to become integrated into nucleohistone during reconstitution in a manner characteristic of the core histones. Purified A24 in solution was shown to exhibit the same specificity of interaction with histone H2B as is exhibited by histone H2A. We conclude that A24 in chromatin replaces H2A as a stable integral component of certain nucleosome histone cores.
