title: Reassembly of nucleosomal histone octamers during replication of chromatin.
abstract: We have examined critically whether or not new and old histones mix in the octameric units of nucleosomes during chromatin replication. MH-134SC cells were density-labeled by culturing with amino acid mixtures enriched with dense isotopes 2H, 13C, and 15N. Mononucleosomes obtained from labeled cells were fractionated by rate zonal sedimentation through a sucrose gradient in heavy water (Senshu et al. (1985) Eur J. Biochem. 150, 575-580). The fractionation can be performed under conditions that do not destabilize nucleosomes. Density-labeling yielded heterogeneous mononucleosome species which showed higher sedimentation rates than normal mononucleosomes. However, they were indistinguishable with respect to their protein compositions, electrophoretic mobilities, electrophoretic patterns of single-stranded DNA fragments liberated by DNase I digestion, electrophoretic mobilities and sedimentation velocities of the DNA moieties, and metabolic stabilities of the histone moieties. These data suggest that the heterogeneity of density-labeled mononucleosomes resulted from the formation of histone octamers density-substituted to different degrees. This would be an inevitable consequence of mixing of new and old histones in the octameric unit of nucleosomes.
mesh_terms: D002478:Cells, Cultured; D002498:Centrifugation; D002843:Chromatin / Q000648:ultrastructure*; D004261:DNA Replication; D006657:Histones / Q000502:physiology*; D046911:Macromolecular Substances; D009024:Morphogenesis; D009707:Nucleosomes / Q000648:ultrastructure*
chemical_list: D002843:Chromatin; D006657:Histones; D046911:Macromolecular Substances; D009707:Nucleosomes