Scheme 1. Schematic Representation of the CAG Ω-DNA Construct.

The positions where a single guanine base was replaced by a tetrahydrofuran abasic site analogue (F) are indicated by the letter X, where X can be either G or F. Also shown are the corresponding designations/names for these modified constructs. Lesion sites upstream (CAG-FStem) or downstream (CTG-FStem) of the loop domain are defined by the orientation shown here. Although the schematic represents the CAG loop domain as unstructured, experimental evidence suggests these bases adopt a structured/base-paired conformation. The nature of the pairing interactions in the loop and at the loop duplex junction is unknown.