title: Conformational properties and thermodynamics of the RNA duplex r(CGCAAAUUUGCG)2: comparison with the DNA analogue d(CGCAAATTTGCG)2.
abstract: The thermodynamic stability of nine dodecamers (four DNA and five RNA) of the same base composition has been compared by UV-melting. TheDeltaG of stabilisation were in the order: r(GACUGAUCAGUC)2>r(CGCAAATTTGCG)2 approximately r(CGCAUAUAUGCG)2>d(CGCAAATTTGCG)2 approximately r(CGCAAAUUUGCG)2>d(CGCATATATGCG)2 approximately d(GACTGATCAGTC)2>r(CGCUUUAAAGCG)2 approximately d(CGCTTTAAAGCG)2. Compared with the mixed sequences, both r(AAAUUU) and r(UUUAAA) are greatly destablising in RNA, whereas in DNA, d(TTTAAA) is destabilising but d(AAATTT) is stabilising, which has been attributed to the formation of a special B'structure involving large propeller twists of the A-T base pairs. The solution structure of the RNA dodecamer r(CGCAAAUUUGCG)2has been determined using NMR and restrained molecular dynamics calculations to assess the conformational reasons for its stability in comparison with d(CGCAAATTTGCG)2. The structures refined to a mean pairwise r.m.s.d. of 0.89+/-0.29 A. The nucleotide conformations are typical of the A family of structures. However, although the helix axis displacement is approximately 4.6 A into the major groove, the rise (3.0 A) and base inclination ( approximately 6 degrees ) are different from standard A form RNA. The extensive base-stacking found in the AAATTT tract of the DNA homologue that is largely responsible for the higher thermodynamic stability of the DNA duplex is reduced in the RNA structure, which may account for its low relative stability.
authors.affiliation: Division of Molecular Structure, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
authors.forename: M R
authors.initials: MR
authors.lastname: Conte
authors.forename: G L
authors.initials: GL
authors.lastname: Conn
authors.forename: T
authors.initials: T
authors.lastname: Brown
authors.forename: A N
authors.initials: AN
authors.lastname: Lane
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry*; D004355:Drug Stability; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009690:Nucleic Acid Conformation; D012313:RNA / Q000737:chemistry*; D012996:Solutions; D013816:Thermodynamics; D014466:Ultraviolet Rays
chemical_list: D012996:Solutions; D012313:RNA; D004247:DNA