THE HIGH-RESOLUTION CRYSTAL-STRUCTURE OF THE DNA DECAMER D(AGGCATGCCT)

The crystal structure of the DNA decamer d(AGGCATGCCT) has been determ ined to a resolution of 1.3 Angstrom and R factor of 13.9%. The struct ure has a unique conformation with each of the decamer single strands forming base-pairing interactions with two symmetry-related strands. T he central eight bases of the decamer form an A-DNA octamer duplex wit h one symmetry-related strand whilst the terminal 5'-A and T-3' bases are flipped out and away from the octamer helix axis to form base-pair ing interactions with a second symmetry-related strand. These A . T ba se-pairs lie perpendicular to the crystallographic c axis and pack wit hin the unit cell in conjunction with a symmetry-related A . T base-pa ir displaced by 3.4 Angstrom along the c axis. A novel base triplet in teraction of the type A(G . C) is present in the structure with inter action from the major groove side of the terminal 5'-A base to the min or groove of the central A-DNA octamer. This structure reports the fir st example of cobalt hexammine binding to a right-handed DNA duplex. T he crystallographic asymmetric unit contains two cobalt hexammine liga nds with one site in the major groove coordinating via hydrogen bonds to the 5'-AGG bases, and the second site located between DNA molecules and interacting with the oxygen atoms of phosphate groups. (C) 1996 A cademic Press Limited