TRANSFER OF THE GENES FOR THE STYLTI RESTRICTION-MODIFICATION SYSTEM OF SALMONELLA-TYPHIMURIUM TO STRAINS LACKING MODIFICATION ABILITY RESULTS IN DEATH OF THE RECIPIENT CELLS AND DEGRADATION OF THEIR DNA

The genes encoding the restriction-modification system StyLTI of Salmonella typhimurium were inserted in vivo into the conjugative plasmid pULB21. This allowed us to transfer the styLTI genes at a very high frequency and to monitor the fate of recipient cells after mating. Transfer of the StyLTI restriction and modification genes into a modificationless recipient was lethal and resulted in degradation of the cell's DNA. This indicates that, in contrast to any other known restriction-modified systems, StyLTI cannot be established after horizontal transfer into a naive host.