Characterization and incompatibility properties of ROM- derivatives of pBR322-based plasmids

We have characterized a copy number mutant of the pBR322-based plasmid pWT111. A single nucleotide transversion in loop II' of RNAI results in an eightfold increase in plasmid copy number. Removal of the rom coding region from pWT111 cop results in a further sixfold increase in copy number. We present evidence that ROM is involved in the strong incompatibility effect seen between pMB1 and ColE1 type plasmids.