The temperate B. subtilis phage phi 105 genome contains at least two distinct regions encoding superinfection immunity.

Two different PstI fragments of temperate phage phi 105 DNA are shown to confer superinfection immunity upon Bacillus subtilis when inserted into the multicopy cloning vector pE194 cop-6. The 2.3 kb PstI fragment I is located almost entirely within EcoRI fragment F and encompasses a region previously known to encode a repressor. The other fragment, PstI-E (4.3 kb) maps inside the EcoRI-B fragment, and allows an explanation of the clear-plaque phenotype of the deletion mutant phi 105DII:6c. The two regions can be distinguished functionally, since only the PstI fragment I product interacts with a specific phi 105 promoter-operator site.