title: Inosine.adenine base pairs in a B-DNA duplex.
abstract: The structure of the synthetic deoxydodecamer d(C-G-C-I-A-A-T-T-A-G-C-G) has been determined by single crystal X-ray diffraction techniques at 2.5A resolution. The refinement converged with a crystallographic residual, R = 0.19 and the location of 64 solvent molecules. The sequence crystallises as a B-DNA helix with 10 Watson-Crick base-pairs (4 A.T. and 6 G.C) and 2 inosine.adenine (I.A) pairs. The present work shows that in the purine.purine base-pairs the adenine adopts syn orientation with respect to the furanose moiety while the inosine is in the trans (anti) orientation. Two hydrogen bonds link the I.A. base-pair, one between N-1(I) and N-7(A), the other between O-6(I) and N-6(A). This bulky purine.purine base-pair is incorporated in the double helix at two positions with little distortion of either local or global conformation. The pairing observed in this study is presented as a model for I.A base-pairs in RNA codon-anticodon interactions and may help explain the thermodynamic stability of inosine containing base-pairs. Conformational parameters and base stacking interactions are presented and where appropriate compared with those of the native compound, d(C-G-C-G-A-A-T-T-C-G-C-G) and with other studies of oligonucleotides containing purine.purine base-pairs.
authors: University Chemical Laboratory, Cambridge, UK.
authors: P W
authors: PW
authors: Corfield
authors: W N
authors: WN
authors: Hunter
authors: T
authors: T
authors: Brown
authors: P
authors: P
authors: Robinson
authors: O
authors: O
authors: Kennard
mesh_terms: D000225:Adenine; D001482:Base Composition; D004247:DNA; D007288:Inosine; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D013237:Stereoisomerism; D014961:X-Ray Diffraction
chemical_list: D007288:Inosine; D004247:DNA; D000225:Adenine