FIG. 5.

SOS response augments the excision rate of the ST64B prophage. A series of isogenic strains defective for Dam methylase or induction of the SOS response were used to monitor the excision rate of ST64B. Bacteria were collected in logarithmic exponential phase after 4 h of growth in LB medium (final OD₆₀₀ of ∼0.3). A culture in parallel of each of the strains was also incubated for the same period of time in the presence of 1 μg ml⁻¹ nalidixic acid (NAL). No changes in the final OD₆₀₀ were registered in untreated versus treated cultures. Shown is the PCR product specific to the excised form of the ST64B genome (sb27-sb28 amplicon) detected in samples of culture supernatants. This series of isogenic strains was constructed in the 14028s genetic background (see Table 1 for details). The assay was repeated three times with similar results.