The DNA methyltransferase (Mtase) genes of temperate Bacillus subtilis phages φ3T, ρ11 and SPβ were cloned and expressed in Escherichia coli. Each gene specifies a 47-kDal protein, which modifies BsuR (GGCC) and Fnu4HI (GCNGC) target sequences. Transcription is controlled by phage promoters located on the cloned fragments. The direction of transcription and the approximate position of the Mtase genes were determined. DNA/DNA hybridization experiments revealed close structural relatedness of the φ3T, ρ11 and SPβ genes. A significant degree of homology was also found among these genes and the Mtase gene of related phage SPR, which codes for an enzyme with different modification specificity. These results suggest a common ancestor of the different phage Mtase genes. Phage Z, the only BsuR-sensitive member of this phage group, lacks a modification gene, but contains regions homologous to sequences flanking the SPR, φ3T, ρ11 and SPβMtase genes. © 1985.
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