Fig. 4. DNA Synthesis during spore germination and recovery to growth phase. Spores were heat-shocked, and allowed to recover in liquid growth media. (A) The increase in nuclei and the peak level of the DNA content profile of mononucleated cells is plotted over the time of the first cell doubling. (B) DNA synthesis was measured by BrdU incorporation as in Fig. 3, using growing cells that had been labeled for one cell cycle as a control. (C) The percentage of chromosomal DNA synthesis in germinating spores relative to one cell cycle of growing cells was estimated from the BrdU incorporation in B. The values are normalized to the amount of chromosomal DNA on the blot, determined by Southern hybridization as described in Fig. 3. At the 30-hour time point, there was 52% the BrdU incorporation observed in growing cells after only a 10% increase in the number of nuclei. At 21-hours, some BrdU incorporation into chromosomal DNA was detectable upon longer exposures of the blot (arrow).