Fig. 4. D copy number with one mutated origin. The maps show an intact miniP1 origin and the regions deleted from one of the origins in mutant plasmid dimers. Open bars represent P1 DNA and arrowheads the iterons as in Figure 1. In the ΔAT mutant plasmid, the H2–N1 region is deleted. The plasmid is also deleted for the ScaI–SspI region of pBR322 DNA containing a bla promoter. In the ΔincC mutant plasmid, the N1–H3 region carrying the incC iterons is deleted. In the Δ(AT+incC) mutant plasmid, the RsaI–H3 region is deleted. Two independent cultures were used for each plasmid. Deletion of the iterons from one of the origins had the most dramatic effect on dimer copy numbers [lanes ΔincC and Δ(AT+incC)].