“…Probes have been identified that react with the Watson-Crick, Hoogsteen, and sugar faces of the base, the ribose sugar, and the phosphate, as reviewed in Ehresmann et al (1987) with recent advances presented in , Spitale et al (2013), Umeyama and Ito (2017), Feng et al (2018), and Mitchell et al (2018). Dimethyl sulfate (DMS) reacts with A(N1) and C(N3) on the Watson-Crick face, as well as G(N7) and A(N3) in the major and minor grooves, respectively, where it has also been used to probe dsDNA (Lawley and Brookes 1963;Umeyama and Ito 2017). Kethoxal is used to probe the Watson-Crick face of G, whereas selective 2 ′ -hydroxyl (2 ′ -OH) acylation analyzed by primer extension (SHAPE) reacts with the 2 ′ -OH ) and light-activated structural examination of RNA (LASER) modifies the C8 position of purines (G>A) (Feng et al 2018).…”