Figure 2.

Genome compartmentalization is similar during all interphase stages. The applied double labeling procedure is schematically drawn at the top. Typical replication labeling patterns were obtained by incorporation of Cy3-dUTP into the DNA of the S phase cells of exponentially growing CHO cultures. 19 h after Cy3-dUTP microinjection, cultures were replication-labeled with BrdU and fixed after 30 min. Cells in S phase at the time point of fixation (BrdU-labeled) can be distinguished from G1 and G2 cells (not BrdU-labeled). The DAPI staining is shown in a (a–c, same field of cells is imaged). Mitotic stages of exponentially growing cultures are indicated by arrowheads. Cy3-labeled cells are depicted in b. Note the two pairs of cells with similar labeling intensities and labeling patterns (upper pair, type I; lower pair, type III; blurred label is due to epifluorescent imaging). Cells of one pair are likely sister cells (compare Fig. 4). The right cells of each pair were in S phase at the time point of fixation (arrows) as indicated by the BrdU label depicted in c. Cy3 labeling patterns are similar in S phase and non-S phase cells.