Fig. 3. (A) Accumulation of biotinylated individual histones: quantitative estimation. All experimental conditions of estimation of cellular uptake are as described in Materials and Methods. An optical density of 0.2 represents 0.47 nmol histone/mg protein. (B) The effect of various inhibitors on the intracellular accumulation of H2A and H4. (a) Accumulation of biotinylated H2A () and H4 () into Colo-205 cells. Cells were pre-incubated before the addition of the histones for 30 minutes at 37°C with the various endocytic inhibitors at the concentrations described in Table 1. The amount of biotinylated H2A and H4 present in the nuclei of cells incubated in 37°C was considered to be 100% and was found to be 5.9 and 5.5 nmol histone/mg protein, respectively. (C) Intracellular accumulation of biotinylated H2A in Colo-205 cells: effect of ATP depletion and unlabelled H2A. Accumulation of biotinylated H2A within the cell cytosol and nuclei was estimated as described in Materials and Methods. ATP depletion was performed as described in Table 1. , nuclei; , cytosol. The amount of biotinylated H2A present in the nuclei of cells incubated in 37°C was considered to be 100% and represents 5.8 nmol/mg protein; it was estimated to be about 48% of the total added histones. The ratio given (in A and C) are in mole:mole.

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