Figure 2

The different transposons used in TRACER. Within the left and right inverted/direct repeats of the SB transposon (black double arrows) different cargoes have been cloned that can be utilised for various purposes. Most lines contain an insertion of either the SB9 or SB8 transposon, comprising a LacZ reporter gene with a SV40 polyA sequence (blue rectangle), driven by a synthetic promoter composed of 50 bp of the human beta-globin promoter (black box with β), and a loxP site (red triangle). Newer transposons with additional features have been constructed, and mice with these transposons are being produced. Additional modules comprise sites for the PhiC31 integrase (attB), and the I-Sce1 meganuclease, which open possibilities to use the transposon as a docking site for incoming cassettes [46–48]. TetO binding sites can be used to recruit fusion proteins [49]. SBIL contains an insulator/enhancer-blocker element (Ins, orange block, from the chicken HSS4 element [50]) flanked by loxP and lox2272 (white triangle with red contour). Cre-mediated recombination can transform this transposon into different derivatives (SBL or SB2lox), depending on which lox sites are used.