Figure 1

The mini-Tnt1 vector system. Mini-Tnt1 is a non-autonomous element that carries a neomycin phosphotransferase gene (NPTII) driven by the nopaline synthase (NOS) promoter. An artificial intron (AI; black box) is present in the NPTII coding sequence. Long terminal repeat (LTR) sequences are shown as open boxes with solid triangles. The 35S-mini-Tnt1 has a cauliflower mosaic virus 35 S promoter that replaces part of the 5' LTR (red). The primer binding site (PBS) and polypurine tract (PPT) are depicted by red bars. Below the 35S-mini-Tnt1 is the element mRNA that undergoes splicing and serves as a template for reverse transcription. To the right of 35S-mini-Tnt1 is an autonomous Tnt1 retrotransposon present in the tobacco genome (not drawn to scale). The autonomous Tnt1 provides GAG and POL in trans to enable transposition of the mini-Tnt1 mRNA. POL gene products include protease (PR), reverse transcriptase (RT) and integrase (IN). The replicated mini-Tnt1 at the bottom of the figure has several features indicative of transposition (red numbers): (1) it lacks an intron,;( 2) it has a complete 5' LTR that is reconstituted during reverse transcription, and (3) it is flanked by a target site duplication (red DNA sequences).