Immunochemical measurement of histone H3 in non‐nucleosomal compartments of cultured mammalian cells

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Abstract
We measured histone H3 in the non-nucleosomal compartment of cultured mammalian cells by enzyme-linked immunoelectrotransfer blot assay of cytosolic proteins using affinity-purified rabbit anti-H3 IgG, and peroxidase-linked second antibodies. The cytosolic H3 level was estimated to be 0.5–1.0% of the nucleosomal H3 content in MH-134SC cells (mean generation time 11 h) and 3–4% in HeLa cells (mean generation time 22 h). It showed characteristic changes under the inhibition of DNA and/or protein synthesis and during the cell cycle of HeLa cells. These indicate an inverse relationship between the cytosolic H3 level and the replicating activity of nuclear DNA. The possible implication of the non-nucleosomal histones in the regulation of histone gene expression is discussed.