INTERACTION BETWEEN THE LEFT-HANDED Z-DNA AND POLYAMINE-2 - THE CRYSTAL-STRUCTURE OF THE D(CG)(3) AND SPERMIDINE COMPLEX

This paper deals with the crystal structure of d(CG)(3)-spermidine com plex, The DNA fragment, d(CG)(3), was crystallized with N-(2-amino-pro pyl)-1,4-diamino-butane, PA(34), spermidine, The results of its X-ray crystallographic analysis showed many intermolecular contacts between d(CG)(3) and spermidine, but the binding mode of spermidine to the d(C G)(3) molecule is different from that of the d(CG)(3) and N-(2-amino-e thyl)-1,4-diamino-butane [PA(24)] complex: a spermidine molecule bound to the d(CG)(3) and its symmetrically related neighboring d(CG)(3) mo lecules through the water molecules with hydrogen bonds, while one PA( 24) molecule connected directly to one d(CG)(3) molecule, but not to i ts neighboring d(CG)(3) molecule, In the crystal, the d(CG)(3) molecul e was the left-handed Z-form, and three magnesium cations and a sodium cation were observed around the d(CG)(3) moiety with different bindin g modes from the case of the d(CG)(3)-PA(24) complex.