Mutational analysis of bacteriophage phi CTX cos site.

The DNA of phi CTX contains the gene ctx, located closely downstream of cos. This encodes for the pore-forming cytotoxin protein, CTX. phi CTX converts some Pseudomonas aeruginosa strains into CTX producers. After different periods of phi CTX infection, two distinct forms of phage DNA were isolated: circular DNA from bacterial cytosol and later linear DNA from phi CTX particles. When circular phi CTX DNA was transfected into the P. aeruginosa strains CF5 and E40, phi CTX was amplified and ctx expressed. phi CTX induced a protein fraction in CF5 cells that cleaved the 0.477 kb cos fragment at the cos site, indicating terminase activity. Deletion and point mutation variants of the cos DNA were prepared. Protein binding to DNA in vitro and competition experiments in vivo showed that portions of the cos site and its flanking sequences are differentially critical to the binding of phi CTX-induced proteins.