Scheme 2. (A) Oligonucleotide Variants Used in This Study; (B) Schematic of the “Static” Repeat Bulge Loop Construct Formed by Combining Oligomers [CAG]₈ with [CTG]₀ (an Eight-CAG Repeat Bulge Loop in One Fixed Arrangement); (C) Schematic of the Different Positional Loop Isomers for Loops That Can Exist in Five Equivalent Loop Arrangements, Here Represented by [CAG]₈·[CTG]₄.

In panel (B), the repeats where an adenine is replaced by 2-aminopurine (2Ap) and a cytosine by pyrollocytosine (PC) in the fluorescently labeled constructs are indicated in pink and green, respectively. In panel (C), the positions of the fluorescent labels and their partitioning in different structural domains for the different rollamers are shown.