Deletion of the D78 cluster increases the ratio of the oriC region to a terminal region and the copy number of the pWHM+D78 plasmid. Total DNA from S. coelicolor M145 and ΔD78, with and without pWHM+D78, was isolated from cultures grown in YEME-tryptic soy broth (26) for 24 h. Southern blots of DNA (3 μg) digested with SalI were hybridized with the labeled probes indicated. The probes consisted of sequences specific for the oriC region (gyrB gene; 500 bp), a chromosome end (argG; 550 bp) (41), and the pWHM3 plasmid (∼500-bp SalI-XhoI fragment of the pWHM3 plasmid). The hybridization signals were quantified by using the ImageQuant program. (A) Quantification of hybridization signals. The graph shows the relative copy numbers of the oriC regions (gyrB) and the chromosomal ends (argG). The locations of the probes on the chromosome are indicated below the graph. (B) (Left panel) Southern blot hybridization. Lane 1, S. coelicolor M145; lane 2, S. coelicolor ΔD78; lane 3, S. coelicolor M145/pWHM3+D78; lane 4, S. coelicolor ΔD78/pWHM3+D78. (Right panel) Quantification of hybridization signals. The graph shows the relative copy numbers of the oriC region (gyrB) and the pWHM3 plasmid. WT, wild type.