FIG. 4.

Effect of externally added DNase on the stability of DNA in heat-treated cells. Cells were incubated for 5 min at 20°C (A), 55°C (B), 72°C (C), or 100°C (D), or for 15 min at 121°C (E) before the temperature was adjusted to 20°C and DNase was added. DNA was quantified by 5′-nuclease PCR after 5, 15, and 30 min and 1, 6, and 24 h at 20°C in both DNase-treated samples and negative controls. The stability of purified DNA treated with DNase was also investigated (F). The amounts of DNA present with (⧫) and without () DNase treatment, are reported as copy numbers relative to those present before heat treatment. The error bars show standard deviations.