Recombinant derivatives of Bacillus subtilis phage Z containing the DNA methyltransferase genes of related methylation-proficient phages.

The DNA methyltransferase (Mtase) genes of temperate Bacillus subtilis phages SPR, phi 3T, SP beta and rho 11 can be transferred by transfection and recombination to the genome of the related non-modifying phage Z. Integration of the Mtase genes occurs in phage Z DNA at a unique location which is homologous with the flanking regions of the Mtase genes of the related phages. In lysogenic cells carrying recombinant phages, expression of the Mtase genes is repressed, irrespective of whether the Mtase genes were derived from phage donors which were homo- or heteroimmune to phage Z.