The GTm6AC sequence is overwound and bent

Abstract
By a combination of distance constraints obtained from NMR spectra and molecular mechanics calculations we have determined the three dimensional structure of the self-complementary decanucleotide d(CGCGTm6ACGCG). Methylation of an adenine at a position 3′ to T induces significant conformational changes relative to B-DNA This arises from the close proximity of the four methyl groups in the large groove in the centre of the sequence. The helical twist between the two T-m6A base pairs is found to be 45′, as for D-DNA, and is accompanied by a high negative value of the wedge roll angle between these base pairs. The overall nonzero wedge roll observed shows that the helix is bent. These contraints appear to be material for the absence of the sequence T-m6A In natural DNAs