Fig. 1: The syn and anti isomers of m6A.

a The m⁶A nucleobase shows a 20:1 preference for the syn isomer due to unfavorable steric interactions (shown in dashed red lines) in the anti isomer^{12, 25}. In a duplex, the syn isomer impedes Watson–Crick pairing, and the anti isomer becomes the dominant form. b Apparent annealing (k_on) and melting (k_off) rate constants for unmethylated (−m⁶A) and methylated (+m⁶A) dsRNA. Rate constants shown were obtained from CEST measurements on dsGGACU with and without m⁶A at T = 65 °C²¹. c Schematic of the general four-state CS + IF model. \({k}_{1}\) and \({k}_{-1}\) are the forward and backward rate constants for methylamino isomerization in ssRNA, respectively; \({k}_{2}\) and \({k}_{-2}\) are the forward and backward rate constants for methylamino isomerization in dsRNA, respectively; \({k}_{{{{{{\mathrm{on}}}}}},{{{{{\mathrm{anti}}}}}}}\) and \({k}_{{{{{{\mathrm{off}}}}}},{{{{{\mathrm{anti}}}}}}}\) are the annealing and melting rate constants, respectively, when m⁶A adopts anti conformation in both ssRNA and dsRNA; \({k}_{{{{{{\mathrm{on}}}}}},syn}\) and \({k}_{{{{{{\mathrm{off}}}}}},syn}\) are the annealing and melting rate constants, respectively when m⁶A adopts syn conformation in both ssRNA and dsRNA.