Studies on plasmid replication. IV. Complementation of replication-defective mutants by an incompatibility-deficient plasmid.

This paper described a complementation test system for replication-defective S. aureus pencillinase plasmids in which the incompatibility barrier has been overcome by the isolation of an incompatibility-defective (Inc-) plasmid. This plasmid appears to be stably and irreversibly integrated into the host chromosome as attempts to restore it to its original independent state have been unsuccessful. The Inc- plasmid was able to complement the thermosensitive replication defects of Seg- plasmids belonging to the same original incompatibility class but was unable to complement onels belonging to a different incompatibility class. Positive and negative phenotypic complementation tests were confirmed at the molecular level by isotopec labeling of plasmid-specific DNA molecules.