SB transposon mapping and Orientation. A) The SB transposon is asymmetric and can map in either + or – orientation within specific TA sites. B) Genomic region after insertion of SB transposon in either + orientation (red) capable of driving transcription of genes encoded on the positive strand or in – orientation (blue) capable of driving genes encoded on the – strand. In either direction a splice site acceptor is available, leading to transcript disruption. PCR products derived from SB junction fragments are capable of determining which orientation the transposon has integrated. The sets of primers i-iv indicate how the PCR products are obtained. Each of the transposon side primers contains a library specific barcode to allow multiplexing during the sequencing process.