Fig. 4. Spatiotemporal replication patterns over the entire macronucleus S phase (approximately 6-8 hours). Mid optical sections of four macronuclei after pulse-chase-pulse labelling with IdU and CldU (pulse, 30 minutes; chase, 2 hours; pulse, 30 minutes) (I-IV) and of one macronucleus after pulse labelling with CldU followed by a 24-hour chase (V). Focal organisation of IdU-labelled post-replicative DNA is preserved even after a total chase of 2.5 hours (chase for 2 hours + second pulse for 30 minutes) or of 4.5 hours (chase for 4 hours + second pulse for 30 minutes; data not shown). These foci still appear as a dispersed band suggesting that mobility of post-replicative foci is strictly limited (II-IV). Focal organisation remains preserved even after amitosis (V), but foci are scattered throughout the entire volume of the macronucleus.