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Journal of Bacteriology, March 2009, p. 1933-1940, Vol. 191, No. 6
0021-9193/09/$08.00+0 doi:10.1128/JB.01537-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Centre de Recherche en Infectiologie, Centre Hospitalier Universitaire de Québec,1 Département de Biochimie et de Microbiologie, Faculté des Sciences et de Génie, Université Laval, Québec, Canada2
Received 30 October 2008/ Accepted 3 January 2009
Integrons are mobile genetic elements that can integrate and disseminate genes as cassettes by a site-specific recombination mechanism. Integrons contain an integrase gene (intI) that carries out recombination by interacting with two different target sites; the attI site in cis with the integrase and the palindromic attC site of a cassette. The plasmid-specified IntI1 excises a greater variety of cassettes (principally antibiotic resistance genes), and has greater activity, than chromosomal integrases. The aim of this study was to analyze the capacity of the chromosomal integron integrase SamIntIA of the environmental bacterium Shewanella amazonensis SB2BT to excise various cassettes and to compare the properties of the wild type with those of mutants that substitute consensus residues of active integron integrases. We show that the SamIntIA integrase is very weakly active in the excision of various cassettes but that the V206R, V206K, and V206H substitutions increase its efficiency for the excision of cassettes. Our results also suggest that the cysteine residue in the β-5 strand is essential to the activity of Shewanella-type integrases, while the cysteine in the β-4 strand is less important for the excision activity.
Published ahead of print on 9 January 2009.
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