PLASMIDS CONTAINING COS ENDS INHIBIT THE REPLICATION OF PHAGE PHI-CTXIN PSEUDOMONAS-AERUGINOSA

In bacteriophage phi CTX, the cohesive end sequences cos, the integras e gene int, the attachment site attP (the target site for int) and the gene ctx encoding a pore-forming cytotoxin CTX, are clustered. phi CT X can infect some Pseudomonas aeruginosa strains with a subsequent ind uction of CTX expression. The 41 and 477 bp fragments containing cos e nds of phi CTX DNA were cloned into the high copy number plasmid pHA 1 0. After pretransformation with the cos ends containing plasmids, plaq ue formation of phi CTX and cytotoxin production in phi CTX-infected P seudomonas aeruginosa cells decreased by 100- and l0-fold respectively . Twelve hours after phi CTX infection proteins binding with cooperati vity to cos sequence containing cleavable ends and the 10 bp flanking sequences were detected by gel electrophoretic mobility retardation of [P-32]cos DNA. The results suggest that the cos binding proteins of p hi CTX are involved in phi CTX replication.