Twist-joints and double twist-joints in RNA structure

B-DTJ: interaction of nucleotide 0R (white) with the major groove of base pair [0P;0Q] (black). The juxtaposition of 0R and 0P can be described as base pair cis-SE-HG. In all cases, there is one hydrogen bond between 0R and 0P. Compared to the equivalent interaction in A-DTJs, the position of base pair [0P;0Q] with respect to nucleotide 0R is under-twisted, which is due to a shorter helix H2 (see also Supplemental Fig. S1).