SUMMARY: Studies involving the introduction of cloned homologous genes into revealed that several plasmids could not be conjugally introduced into 775(pJM1), but were transmissible to the pJM1-cured derivative H775-3. Recombinant pBR322 plasmids containing genomic DNA inserts were mobilized from donors, using pRK2013, into H775–3 recipients at frequencies of 10 to 10 per recipient. When identical matings were performed with 775(pJM1) recipients, the infrequent exconjugants recovered carried the pBR322-based plasmid but had lost the large virulence plasmid pJM1. Similar studies were carried out with plasmid RP4 and with recombinant derivatives of the closely related broad-host-range plasmid pRK290. While RP4 was transmissible from to H775–3 at frequencies of 6.7 × 10 per recipient, transmission to 775(pJM1) recipients occurred at frequencies of only 2.5 × 10. When pRK290 contained DNA inserts, the only exconjugants recovered had lost pJM1, or contained pJM1 and a deletion derivative of the recombinant pRK290 plasmid where all of the DNA insert had been deleted. The use of Dam, Dcm, or K methylation-deficient donor strains failed to result in appreciable numbers of 775(pJM1) exconjugants that contained the desired transferred plasmids. Following UV mutagenesis, a derivative of 775(pJM1) was isolated that would accept conjugally transferred plasmid DNAs at frequencies similar to those observed when using H775–3 recipients. These data suggest that virulence plasmid pJM1 mediates a restriction system that prevents conjugal transmission of plasmid DNA from donors into 775(pJM1). This putative restriction system appears not to be directed towards Dam-, Dem-, or K-methylated DNA, and appears not to involve a Type II restriction endonuclease.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error