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Journal of Bacteriology, March 2002, p. 1712-1721, Vol. 184, No. 6
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.6.1712-1721.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

IntI2 Integron Integrase in Tn7

Karin Hansson,1 Lars Sundström,1 Alex Pelletier,2,3 and Paul H. Roy1,2,3*

Department of Pharmaceutical Biosciences, Division of Microbiology, Uppsala University, Uppsala, Sweden ,1 Département de Biochimie, Faculté des Sciences et Génie, Université Laval,2 Centre de Recherche en Infectiologie, Centre Hospitalier Universitaire du Québec, Ste-Foy, Quebec, G1V 4G2 Canada3

Received 10 September 2001/ Accepted 10 December 2001

Integrons can insert and excise antibiotic resistance genes on plasmids in bacteria by site-specific recombination. Class 1 integrons code for an integrase, IntI1 (337 amino acids in length), and are generally borne on elements derived from Tn5090, such as that found in the central part of Tn21. A second class of integron is found on transposon Tn7 and its relatives. We have completed the sequence of the Tn7 integrase gene, intI2, which contains an internal stop codon. This codon was found to be conserved among intI2 genes on three other Tn7-like transposons harboring different cassettes. The predicted peptide sequence (IntI2*) is 325 amino acids long and is 46% identical to IntI1. In order to detect recombination activity, the internal stop codon at position 179 in the parental allele was changed to a triplet coding for glutamic acid. The sequences flanking the cassette arrays in the class 1 and 2 integrons are not closely related, but a common pool of mobile cassettes is used by the different integron classes; two of the three antibiotic resistance cassettes on Tn7 and its close relatives are also found in various class 1 integrons. We also observed a fourth excisable cassette downstream of those described previously in Tn7. The fourth cassette encodes a 165-amino-acid protein of unknown function with 6.5 contiguous repeats of a sequence coding for 7 amino acids. IntI2*179E promoted site-specific excision of each of the cassettes in Tn7 at different frequencies. The integrases from Tn21 and Tn7 showed limited cross-specificity in that IntI1 could excise all cassettes from both Tn21 and Tn7. However, we did not observe a corresponding excision of the aadA1 cassette from Tn21 by IntI2*179E.

* Corresponding author. Mailing address: Centre de Recherche en Infectiologie, CHUQ Pavillon CHUL, 2705 Blvd. Laurier, Suite RC-709, Ste-Foy, Quebec G1V 4G2, Canada. Phone: (418) 654-2705. Fax: (418) 654-2715. E-mail: Paul.H.Roy{at}crchul.ulaval.ca.

Journal of Bacteriology, March 2002, p. 1712-1721, Vol. 184, No. 6
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.6.1712-1721.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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Copyright © 2002 by the American Society for Microbiology. All rights reserved.