Figure 5.

Fluorescence-detected thermal denaturation of the 2Ap/PC-labeled [CAG]₈·[CTG]₄ construct (four-repeat loop, five arrangements) containing a THF abasic site lesion between the fluorophores within the triplet repeat sequence, with melting monitored at (A) the 2Ap excitation/emission maximum (305 nm/370 nm) and (B) the PC excitation/emission maximum (340 nm/460 nm). To facilitate comparisons, these curves have been scaled/normalized such that the fluorescence of the fully denatured complexes at 90 °C is equal to 1. The same initial irreversible transition (light-red curve) observed in the first heating but absent during subsequent heating/cooling steps (light-blue and dark-red) as seen in Figure 4 is present. Also noteworthy is the gradual decrease in 2Ap fluorescence intensity at temperatures near or above the initial irreversible transition detected in the first heating, which is coupled with a gradual increase in PC fluorescence. These gradual fluorescence changes occur at temperatures much lower than the temperatures where denaturation is detected by temperature-dependent UV absorption measurements, suggestive of increased loop migration (rollamerization) at these temperatures.