The structure of the most studied DNA fragment changes under the influence of ions: a new packing of d(CGCGAATTCGCG)

AbstractThe title oligonucleotide and many related dodecamers have been extensively studied alone and as DNA-drug complexes. In practically all cases they were found to crystallize in the same space group, stabilized by interactions among the terminal guanine bases. Here we report new packing interactions (R3) in the presence of Ca2+. The oligonucleotides interact by placing their terminal guanines in the narrow groove of a neighbor molecule, an interaction which had never been found in dodecamers