Lack of substantial sequence homology between the cryptic plasmid and chromosome of Neisseria gonorrhoeae.

Previous reports have suggested that either large segments of the 4.2-kb phenotypically cryptic plasmid or the entire plasmid are integrated into the chromosome of Neisseria gonorrhoeae, even in rare plasmid-free strains. A series of subclones of the cryptic plasmid have been used in Southern blotting experiments to map the extent of this hybridization with the chromosome. Hybridization could only be detected at low or medium stringency, and the data suggest the absence of entire plasmids, or even large contiguous sections of the cryptic plasmid, in the chromosome of N. gonorrhoeae. In confirmation of this, a chromosomal fragment that hybridizes to the cryptic plasmid was cloned and sequenced. The low stringency hybridization between the cryptic plasmid and chromosome seems to be the result of short repetitive sequences found in both DNA molecules, rather than full or partial plasmid integration.