Figure 8.

Compartmentaliza-tion of transcriptionally competent chromatin in nuclei of CHO and HeLa S6 cells. Nuclei were replication-labeled with Cy3-dUTP (depicted in red). Cells were fixed and immunostained with R232/8 antiserum (FITC-detected, depicted in green) 23 (a–f, j, and k) or 1 h (g–i, l) after replication labeling. a–i display images of CHO nuclei, whereas j–l show HeLa S6 nuclei. For each nucleus, single light optical sections of identical midnuclear planes regarding Cy3 and FITC fluorescence detection are shown. For all distinct nuclei (a–c, d–f, g–i, and j and k or l correspond to one nucleus) the FITC (c, f, and i), Cy3 (b, e, and h) and merged signals (a, d, and g) are shown except for j–l where only the merged signals of different nuclei are depicted. Colocalizing FITC and Cy3 signals appear yellow on merged images. Chromatin enriched in highly acetylated isoforms of histone H4 (H4Ac), indicated by R232/8 staining (green), is concentrated in the interior compartment (a, b, and j, colocalizing with the type I pattern, red). R232/8 staining is excluded from the peripheral and late replicating compartments (d, e, g, h, k, and l, replication-labeled, red).