Figure 1
Generation of an RNA duplex by crystallographic symmetry. (a) In the H32:R crystal, the single chain in the asymmetric unit (blue) and its symmetry mate (yellow) related by a crystallographic twofold axis generate a double-stranded antiparallel RNA duplex (highlighted in more saturated colours) in which the two chains in the duplex overlap by 18 ribonucleotides, as illustrated schematically in (b). C19 and G20 overlap with the next duplex to generate a continuous A-type RNA double helix along a crystallographic 31 axis. In addition to the canonical base pairings C2–G18, A6–U14, U8–A12 and U9–A11, there is a classic wobble G7–U13 pair together with C3–A17, U4–U16 and C10–C10 noncanonical pairs. |