Figure 1.

Alkaline sucrose density gradient centrifugation (ASDG) profiles of replication products in UV‐irradiated (a,c) NB1RGB (normal) and (b,d) HeLa cells. (a,b) Time‐course of elongation, (c,d) effect of caffeine. Cells synchronized in the mid‐S phase were UV (10 J/m²)‐irradiated, incubated in normal medium for 30 min, pulse‐labeled with 10 µCi/mL of [¹⁴C]thymidine for 1 h, washed twice with phosphate‐buffered saline (PBS), and incubated for 1–5 h at 37°C in a normal medium containing (c,d) 1.25–10 mM caffeine, or (a,b) no inhibitor. (c) Some of these profiles overlap. Sedimentation is from right to left. The arrow indicates the position of the T4 phage DNA (166 kb, i.e. approximately 5.5 × 10⁷ Da/single strand). Labeled E. coli DNA (approximately 4 Mb) sedimented near the bottom (fractions 3–6).^{( 4 )} The average fragment length (in Mb) of each profile is shown in square brackets. cpm, counts per minute.