Figure 2.

Enzyme digestion to confirm the plasmid substrate containing an ICL. Lanes 1, 4, 7: supercoiled plasmids with no treatment; lanes 2, 5, 8: plasmids treated with SalI; lanes 3, 6, 9: plasmids treated with BglII. Duplex plasmid can be cut by both SalI and BglII (lanes 2 and 3), but the plasmid with the p-ss-TFO-ICL is resistant to both SalI and BglII digestion (lanes 5 and 6). However, if a plasmid containing a p-ss-TFO-ICL is treated with DTT, the plasmid can be cut by BglII (linearized band in Lane 9), but not by the SalI enzyme (Lane 8). This indicated that TFO1 had been removed by DTT treatment and the psoralen ICL was still present at the SalI restriction site.