SEQUENCE-DEPENDENT CROSSED HELIX PACKING IN THE CRYSTAL-STRUCTURE OF A B-DNA DECAMER YIELDS A DETAILED MODEL FOR THE HOLLIDAY JUNCTION

The structure of the B-DNA decamer d(CGCAATTGCG)(2) has been determine d by X-ray diffraction analysis to a resolution of 2.3 Angstrom and an R-factor of 17.7%. The decamer crystallises in the monoclinic space g roup C2 and packs with a crossed arrangement of helices and a unique c rossing contact distinct from all other decamer structures. This is be lieved to be a direct result of the sequence-dependent minor groove wi dth of the duplex. Crossed helix structures of DNA are valuable starti ng points for modelling studies of the Holliday junction. Two unique s ites are observed at the cross-over junction where strand exchange may occur. A Holliday junction model has been constructed for each case a nd modelled using molecular mechanics and dynamics techniques. One of these models was found to be fully consistent with the available physi cal data. (C) 1997 Academic Press Limited.