Figure 1.

Early and revised r(U₅UCG₈) NMR model structures. (a) First NMR structural signature (adapted with permission from [18]). (b) First model of the U•G pair in an r(UUCG) loop (adapted with permission from [19]). (c) The preceding model was revised in 1995 to lead to the correct trans-Sugar/Watson-Crick (tSW) base pair arrangement (adapted with permission from [22]). Note that a C•G tSW pair would be perfectly isosteric to the U•G tSW pair. (d) A C7…U5 base…phosphate interaction, annotated as 8BPh, is part of the r(UUCG) tetraloop signature (adapted with permission from [18]).