Larouche André, Roy Paul H
Centre de Recherche en Infectiologie, Centre Hospitalier Universitaire de Québec, Québec, Canada.
J Bacteriol. 2009 Mar;191(6):1933-40. doi: 10.1128/JB.01537-08. Epub 2009 Jan 9.
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 beta-5 strand is essential to the activity of Shewanella-type integrases, while the cysteine in the beta-4 strand is less important for the excision activity.
整合子是可移动的遗传元件，能够通过位点特异性重组机制将基因作为盒式结构进行整合和传播。整合子包含一个整合酶基因（intI），该基因通过与两个不同的靶位点相互作用来进行重组；一个是与整合酶顺式排列的attI位点，另一个是盒式结构的回文attC位点。与染色体整合酶相比，质粒指定的IntI1能够切除更多种类的盒式结构（主要是抗生素抗性基因），并且具有更高的活性。本研究的目的是分析环境细菌亚马逊希瓦氏菌SB2BT的染色体整合子整合酶SamIntIA切除各种盒式结构的能力，并比较野生型与替代活性整合子整合酶共有残基的突变体的特性。我们发现SamIntIA整合酶在切除各种盒式结构方面活性非常低，但V206R、V206K和V206H替代增加了其切除盒式结构的效率。我们的结果还表明，β-5链中的半胱氨酸残基对于希瓦氏菌型整合酶的活性至关重要，而β-4链中的半胱氨酸对切除活性的重要性较低。
