Published online by Cambridge University Press: 14 April 2009
The R factors, R56 and R64, interfere with the growth of several otherwise unrelated phages, including λ, P22 and T7. In addition, λvir is inhibited more strongly in λ lysogens carrying either R factor when the prophage has an intact O – P region. Interference does not occur in certain str A R+ hosts but may reappear if they also carry other mutations affecting ribosomal proteins. Host mutants not permitting interference were isolated but were not strA. Non-interfering plasmid mutants were also isolated, of which some also failed to cause interference after transfer to a different host genus.