Figure 3.

Copy numbers of oriC plasmids carrying promoter mutations. polA1 cells (AQ2178) were transformed with the indicated modified oriC plasmids and grown in the presence of chloramphenicol (50 μg/ml). Total DNA was extracted from exponentially growing cells and digested with PstI and electrophoresed in a 0.8% agarose gel. DNA was blotted, and probed with a 714-bp MluI(−2343) to MluI(−3057) ³²P-labeled oriC DNA fragment. Band intensities were quantified by using a PhosphorImager, and the plasmid-to-chromosome ratio relative to pDB101 is indicated under each lane. For relevant genotypes of plasmids, see Table 2. Control lane is untransformed AQ2178.