Crystal structures of disordered Z-type helices
Authors state that the packing requirement imposes statistical disorder in the molecule leading to only a portion of the molecule to be present in asymmetric unit. Hence the terminal phosphate atoms appears to be in close contact with the symmetry related terminal oxygens.
1mM DNA, 50mM sodium cacodylate trihydrate buffer, 200mM MgSO4, 50% MPD.
A decamer with alternate pyr-pur repeat and TA at the centre
Crystal packing disorder of ZDNA studied by X-ray Crystallography
It has to be noted that limited resolution data was available to refine the highly disordered molecules. The atomic coordinates are best interpreted for the data to a resolution of 2.5 A and the electron density map is justified for this highly disordered in packing Z-type helices in which exocyclic atoms of the pyrimidine bases and backbone phosphate groups are refined with partial occupancies.
Tetradecamer sequence, alternate pyr-pur repeat, left handed Z-DNA duplex, discontinuous helices, P3(2), DNA