MOLECULAR ANALYSIS OF A CYTOTOXIN-CONVERTING PHAGE, CIRCLE-DOT-CTX, OF PSEUDOMONAS-AERUGINOSA - STRUCTURE OF THE ATTP COS CTX REGION AND INTEGRATION INTO THE SERINE TRANSFER-RNA GENE

The Pseudomonas aeruginosa ctx gene encoding cytotoxin is carried by a temperate phage phiCTX. The genome of phiCTX is a 35.5 kb double-stranded DNA with cohesive ends (cos). It is unique in that the ctx gene and attP site of phiCTX exist very close to the respective cohesive ends. In this study, we determined the structure of this attP-cos-ctx region. The termini of phiCTX are 21-base 5' extended-single-stranded DNAs. The ctx gene is located 361 bp down-stream of the left end (cosL). The attP core sequence of 30bp exists only 647bp apart from the right end (cosR). The attP-cos-ctx region contains six kinds of repeats and integration host factor-binding sequences and showed sequence-directed static bends, suggesting its potential to form a highly ordered structure. In addition, phiCTX was found to integrate into the serine tRNA gene which was mapped to the 43-45 min region on the P. aeruginosa chromosome.