Presence of protein A24 in rat liver nucleosomes.

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Abstract
Two-dimensional gel profiles of the 0.2 M H2SO4-soluble proteins of monomer nucleosomal fractions contained protein A24. Protein A24 is of interest because it is composed of histone 2A and ubiquitin, apparently joined by an isopeptide linkage. Monomer nucleosomal fractions were obtained by sucrose density gradient centrifugation of micrococcal nuclease digests of rat liver nuclei. As shown by their DNA size, the monomer fractions were highly purified. Proteins A24 and Bu, another protein of unknown characteristics, were found along with histones 1, 2A, 2B, 3 and 4 in the monomer fractions in relative amounts similar to those found in extracts from whole nuclei and chromatin. Other acid-soluble proteins found in the nuclear and chromatin extracts were essentially absent from the monomer fraction. Inasmuch as protein A24 and Bu were found in lesser amounts than the histones, they are probably associated with specialized subsets of nucleosomes.