All 13 TA loci in the mega-integron of V.cholerae Chromosome II have juxtaposed attC sites. (A) The locations of the 13 TA loci in the V.cholera mega-integron are shown relative to the closest attC site. Arrows indicate direction of transcription of the TA operons. The boundaries of the integron were determined here by the Int4 integrase gene and the right-most attC site (attC-R). attC-L is the leftmost attC site of a total of ∼150 attC sites of the integron. (B) Nucleotide sequences of the attC sites [123 bp elements with inverted repeats at their ends as defined in ()] located near TA loci in the V.cholerae mega-integron. The coordinates of the attC sites in the V.cholerae genome and their distances to the TA structural genes (start codons of antitoxin genes or stop codons of toxin genes): attC1: 322548..322671, +14 bp; attC2: 327878..328000, +17 bp; attC3: 343101..343224C, +18 bp; attC4: 349509..349631, −3 bp; attC5: 365215..365336, +15 bp; attC6: 369203..369325, +35 bp; attC7: 388220..388342, −80 bp; attC8: 399166..399288, +7 bp; attC9: 415580..415701, −2 bp; attC10: 417953..418074, +18 bp; attC11: 420535..420656, +6 bp; attC12: 426191..426312, +6 bp; attC13: 432894..433016, +18 bp). In all cases but two (higBA-1 and phd/doc-1), the attC sites were located downstream and close to the toxin structural genes.