The contribution of plasmid and host genes to plasmid-mediated interference with phage growth

SUMMARY The R factors, R56 and R64, interfere with the growth of several otherwise unrelated phages, including λ, P22 and T7. In addition, λviris inhibited more strongly in λ lysogens carrying either R factor when the prophage has an intact O – P region. Interference does not occur in certainstr AR+hosts but may reappear if they also carry other mutations affecting ribosomal proteins. Host mutants not permitting interference were isolated but were notstrA. Non-interfering plasmid mutants were also isolated, of which some also failed to cause interference after transfer to a different host genus.