Figure 7.

Early replication foci and transcription sites have common structural features. Synchronized cells encapsulated in agarose microbeads were grown in medium containing BrdU for 20 min either at the beginning of S phase (A) or 3 h later (B). Samples were extracted with 2 M NaCl and Br-DNA indirectly immunolabeled with FITC. G1 phase cells were grown in medium supplemented with BrU for 5 min and transcription sites labeled in the same way (C). Hypertonic extraction removes histones and spreads ∼60% DNA into a “halo” that surrounds the remnant nuclear matrix (D; DAPI staining of C). Bar, 2 μm.