FIG. 6.

Plasmid topology is not affected by the Δfis or nusB5 mutations. (A) pBR322-derivative pRLG770 (34) was extracted from wild-type (WT), Δfis, and nusB5 strains grown as described in the legend for Fig. 3. The samples in the two lanes shown for each strain derived from duplicate cultures. The DNA in lane N was isolated from a wild-type strain treated with the gyrase inhibitor norfloxacin (10 μg/ml for 30 min) prior to plasmid extraction and electrophoresis on chloroquine gels (see Materials and Methods). In these gels, more relaxed plasmids (R) migrate faster than supercoiled plasmids (SC), as reported previously (11). Topoisomers were quantified using ImageQuant 5.1 (Molecular Dynamics). Representative traces comparing plasmid DNA from Δfis versus wild-type strains (B) and nusB5 versus wild-type strains (C) are shown.