Stereoscopic view of the first crystal structure of a four-stranded intercalated DNA: d(C4). Two parallel duplexes with C:CH+ pairs are intercalated into each other. The purple pair has its 5' ends at the bottom of the diagram, while the green pair has its 5' ends at the top. The numbers refer to the nucleotide number at the 5' end of the strand. Strands C1-C4 are parallel to C5-C8. The two green strands are parallel to each other but are oriented in the opposite direction. The view is from the major groove.