
Molecular model for two adjacent helical 5′ pA's paired to a helical, 3′-5′ oligo U tract. p(U)4 is shown on the left, and two anteparallel pA on the right. Thin red lines between A's and U bases mark H-bonds. Approach of oxygen and phosphate atoms in the two pA's is indicated by the dashed yellow line on the right.










