Structure of the DNA decamer d(GGCAATTGCG) contains both major- and minor-groove binding G.(G.C) base triplets.

The crystal structure of the decamer d(GGCAATTGCG) has been determined at 2.4 A resolution. The central eight bases of each DNA single-strand base pair with a self-complementary strand to form an octamer B-DNA duplex. These duplexes lie end-to-end within the unit cell. The terminal 5'-G and G-3' bases of each decamer strand are unpaired, and interact with the neighbouring duplexes via interactions within both the major and minor groove. This results in base triplets of the type G-(G.C) and G*(G.C), with the third guanine base binding to a Watson-Crick G.C base pair from the major groove and the minor groove, respectively. The triplet interaction of the type G-(G.C) involves Hoogsteen hydrogen-bonding interactions between the two guanine bases. The minor- and major-groove base triplet interactions which exist within this structure act to stabilize the d(GCAATTGC)2 B-DNA octamer duplex.