MUTATIONAL ANALYSIS OF BACTERIOPHAGE-PHI-CTX COS SITE

The DNA of phi CTX contains the gene ctx, located closely downstream o f cos. This encodes for the pore-forming cytotoxin protein, CTX. phi C TX converts some Pseudomonas aeruginosa strains into CTX producers. Af ter different periods of phi CTX infection, two distinct forms of phag e DNA were isolated: circular DNA from bacterial cytosol and later lin ear DNA from phi CTX particles. When circular phi CTX DNA was transfec ted into the P. aeruginosa strains CF5 and E40, phi CTX was amplified and ctx expressed. phi CTX induced a protein fraction in CF5 cells tha t cleaved the 0.477 kb cos fragment at the cos site, indicating termin ase 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 sequenc es are differentially critical to the binding of phi CTX-induced prote ins. Copyright (C) 1996 Elsevier Science B.V.