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. Author manuscript; available in PMC: 2011 Jun 1.

Published in final edited form as: Curr Opin Struct Biol. 2010 Apr 8;20(3):262–275. doi: 10.1016/j.sbi.2010.03.001

A simpler nucleic acid and the structural origins of cross-pairing between different nucleic acid systems or the absence thereof. (a) Crystal structure of S-GNA [83••] (2jja). Carbon atoms of the glycol and 2,6-dipicolinate (Dipic) as well as pyridine (Py) moieties are highlighted in green and copper ions that induce pairing between Dipic and Py are orange. (b) The backbones in both RNA and S-GNA are negatively inclined relative to the base-pair planes [87•] and both are right-handed: Pairing occurs. Unlike in RNA, the backbone-base inclination angle η_B in homo-DNA is positive: No pairing.

A simpler nucleic acid and the structural origins of cross-pairing between different nucleic acid systems or the absence thereof. (a) Crystal structure of S-GNA [83••] (2jja). Carbon atoms of the glycol and 2,6-dipicolinate (Dipic) as well as pyridine (Py) moieties are highlighted in green and copper ions that induce pairing between Dipic and Py are orange. (b) The backbones in both RNA and S-GNA are negatively inclined relative to the base-pair planes [87•] and both are right-handed: Pairing occurs. Unlike in RNA, the backbone-base inclination angle η_B in homo-DNA is positive: No pairing.