Detection of Gene Cassettes in Tn402-Like Class 1 Integrons

Context of gene cassettes in class 1 integrons. (A) Types of class 1 integron structure. Tall vertical bars represent the inverted repeats, and the various backbone segments, 5′-CS, 3′-CS, and the tni module, are represented by lines of different thicknesses. The short vertical bar represents the res site. Open vertical bars represent the attI site of class 1 integrons. Insertion sequences (IS) are shown as open boxes with the IS number above. Genes are indicated by arrows with gene names below. Positions of the primers used here are marked by flags with the primer name adjacent. L1 (5′-GGCATCCAAGCAGCAAGC-3′) and R1 (5′-AAGCAGACTTGACCTGAT-3′) (corresponding to primers 1 and 2 in reference 8) are representative of primer pairs used to amplify cassette arrays. (B) Cassettes in Tn402 and rearranged derivatives. The SphI-BamHI fragment of Tn402 present in pRMH532 is shown together with the cassette arrays present in the various derivatives recovered in this study. Cassettes are shown as open boxes with a vertical bar (representing the 59-be) at one end. (C) PCR amplification of gene cassettes using primer L1 with primer RH506. Lanes: 1, 1-kb markers; 2, pRMH532; 3, pRMH545; 4, pRMH542; 5, pRMH544; 6, pRMH543; 7, 100-bp markers. Predicted sizes of PCR products are 1,524 bp for pRMH532 and 924, 801, 617, and 534 bp for pRMH545, pRMH542, pRMH544, and pRMH543, respectively.