Cloning and characterization of the c1 repressor of Pseudomonas aeruginosa bacteriophage D3: a functional analog of phage lambda cI protein.

We cloned the gene (c1) which encodes the repressor of vegetative function of Pseudomonas aeruginosa bacteriophage D3. The cloned gene was shown to inhibit plating of D3 and the induction of D3 lysogens by UV irradiation. The efficiency of plating and prophage induction of the heteroimmune P. aeruginosa phage F116L were not affected by the presence of the cloned c1 gene of D3. When the D3 DNA fragment containing c1 was subcloned into pBR322 and introduced into Escherichia coli, it was shown to specifically inhibit the plating of phage lambda and the induction of the lambda prophage by mitomycin C. The plating of lambda imm434 phage was not affected. Analysis in minicells indicated that these effects correspond to the presence of a plasmid-encoded protein of 36,000 molecular weight. These data suggest the possibility that coliphage lambda and the P. aeruginosa phage D3 evolved from a common ancestor. The conservation of the functional similarities of their repressors may have occurred because of the advantage to these temperate phages of capitalizing on the potential of the evolutionarily conserved RecA protein to monitor the level of damage to the host genome.