Fig. 7. The ability of caffeine to rescue replication time decreases with time. (A) Sperm nuclei were incubated at 15 ng DNA µl^-1 in extract supplemented with [-³²P]dATP and 15 µM aphidicolin. At the indicated times, 5 mM caffeine plus or minus 0.5 mM roscovitine were added to the extract and the samples incubated for a further 120 minutes, when total DNA synthesis was measured. As a control, aphidicolin was substituted with DMSO. (B) Sperm nuclei were incubated at 15 ng DNA µl^-1 in extract supplemented with [-³²P]dATP and 10 µM aphidicolin, plus or minus 5 mM caffeine and increasing concentrations of His6-N-Cyclin A (Ncyclin A). At 120 minutes total DNA synthesis was measured.