Single-molecule FRET trajectories showing conformational dynamics were analyzed using hidden Markov modeling (HMM) with the variational Bayesian expectation maximization technique (Figure 1B and Supplementary Figure S1) (34,35). The dwell times corresponding to each G4 conformational state were selected based on the plot of dwell times against transfer efficiency (Supplementary Figure S2). To avoid artefacts of the HMM analysis only the states with dwell times longer than two frames were included in further analysis.