Extra-helical guanine interactions in DNA

We review the extra-helical guanine interactions present in many oligonucle otide crystals. Very often terminal guanines interact with other guanines i n the minor groove of neighboring oligonucleotides through N-2. N-3 hydroge n bonds. In other cases the interaction occurs with the help of Ni2+ ions. Guanine/netropsin stacking in the minor groove has also been found. From th ese studies we conclude that guanine may have multiple extra-helical intera ctions. In particular it may be considered a very effective minor groove bi nder, which could be used in the design of sequence selective binding drugs . Interactions through the major groove are seldom encountered, but might b e present when DNA is stretched. Such interactions are also analyzed, since they might be important for homologous chromosome pairing during meiosis. (C) 2000 Elsevier Science B.V. All rights reserved.