DNA sequence of direct repeats of the sulI gene of plasmid pSa.

The restriction enzyme and genetic map of the antibiotic-resistance region of plasmid pSa is related to Tn21 integrons by the insertion of 5.4 kb containing a chloramphenicol resistance gene (catII) and a 1.1-kb direct repeat. We report here the nucleotide sequences of both copies of the repeat with adjoining sequences. They were identical for 1065 bp and contained the entire coding sequence of the sulfanilamide resistance gene, sulI. Since only the first copy of the repeat confers sulfonamide resistance, this leads to the conclusion that no promoter was available for the second copy. The sequence of the pSa sulI gene was identical to several published sulI sequences from other plasmids. The first junction point of the catII-containing insert was identical to the sequence for pDG0100; the second junction occurred farther into the 3'-conserved segment of integrons than does that of pDG0100. A recent report of these junction sequences for pSa and pDG0100 differs from our sequences by one nucleotide. Two additional differences were an insert of 41 bases and a single base insertion between sulI and ORF341 in our sequence. Our sequenced regions have been assigned GenBank Accession Nos. UO4277 and UO4278 for the first and second sulI genes of pSa, respectively.