Figure 1. Triplex formation by the PPG substituted TFOs. (A) The G-rich TFO, AG30 was designed to bind to a polypurine sequence at position 167–196 of the supFG1 reporter gene. The sequence of AG30 and its target duplex site is included. (B) Structure of the natural guanine base compared with the modified base 8-aza-7-deaza-guanine (PPG) base. (C) Design of the 30-mer G-rich TFOs. The G represents PPG.