Light and Electron Microscope Immunocytochemical Analyses of Histone H1(0) Distribution in the Nucleus of Friend Erythroleukemia Cells

The localization of histone H1(0) in murine erythroleukemia cells which were induced to resume a differentiation program was studied in cells which have recovered their proliferative capacity after transient blockage in the G1 phase of the cell cycle. Previous studies have shown that histone H1(0) accumulation occurs at early times of induction and is probably related to the commitment itself. The distribution of the protein was determined by immunomicroscopy with monoclonal antibodies specific for histone H1(0). Our observations showed that the histone accumulates in nuclei. Immunoelectron microscopy further demonstrated the presence of histone H1(0) in condensed chromatin areas, including perinucleolar chromatin. Moreover, histone H1(0) also occurred in the perichromatin regions, previously described as preferential sites of pre-mRNA synthesis, suggesting that histone H1(0) is not fully excluded from active chromatin.