Fig. 1. The distribution of nuclear DNA replication sites in primary, immortalized and transformed mammalian cells follows identical spatio-temporal patterns during S-phase. Cell cultures synchronized at different stages of S-phase after release from aphidicolin block [5 min (G1/S), 1 hour, 2 hours and 4 hours (early-S), 6 hours and 8 hours (mid-S), 10 hours and 12 hours (late-S)] were pulse-labeled for 5 minutes with 30 µg/ml BrdU, fixed and sites of BrdU incorporation were detected with a nuclease/anti-BrdU cocktail. Based on the number, size, shape and distribution of fluorescent foci, the replication sites were classified into five major types of patterns, which were similar in all cell lines.

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