Inosine.adenine base pairs in a B-DNA duplex

Open Access
Publisher Website
Google Scholar
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 0-6(I) and N-6(I). This bulky prine.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.