The role of minor groove functional groups in DNA hydration.

Here we describe the crystal structure of modified [d(CGCGAATTCGCG)]2 refined to 2.04 A. The modification, which affects only the two thymines at the central ApT step, involves isosteric removal of the 2-keto oxygen atoms and substitution of the N1 nitrogen with carbon. The crystal structure reveals the ability of this modified thymine to effectively base pair with adenine in [d(CGCGAAtTCGCG)]2. The structure also suggests that the minor groove 'spine of hydration' is destabilized but essentially intact.