First, we used a mutant telomeric sequence (hTelo-m) (AGGG(CTAGGG)3), which primarily forms an anti-parallel chair conformation in the presence of KCl (41). As expected, one major population is observed in the FRET histogram (Figure 2A). The peak is centered at E≈0.85, which is characteristic for the chair conformation, as previously found in similar buffer conditions (30). The highest FRET state (E≈0.88) of hTelo has a very similar FRET value, strongly indicating that this E state corresponds to the chair conformation.