Mutational analysis of bacteriophage φCTX cos site

Abstract The DNA of φCTX contains the gene ctx , located closely downstream of cos . This encodes for the pore-forming cytotoxin protein, CTX. φCTX converts some Pseudomonas aeruginosa strains into CTX producer. After different periods of φCTX infection, two distinct forms of phage DNA were isolated: circular DNA from bacterial cytosol and later linear DNA from φCTX particles. When circular φCTX DNA was transfected into the P. aeruginosa strains CF5 and E40, φCTX was amplified and ctx expressed. φCTX 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 φCTX-induced proteins.