English: A hypothetical, speculative model of the fully-intercalated Wu "Straight Ladder" DNA structure. The structure consists of a complex between two Watson-Crick-like duplexes. Each one is stretched out to its full length, which removes the helical twist entirely, and results in a large base pair spacing of 6.8 angstroms; twice the usual amount. The two duplexes are then pushed together by mutual intercalation of their base pairs. It is not easy to discern the two duplexes after merging them, but their presence is betrayed by the four sugar-phosphate backbones (Watson-Crick double-helical DNA only has only two strands, and hence only two sugar-phosphate backbones). A complete description of the structure may be found at Biegeleisen K, Probable structure of the protamine-DNA complex, J Theoret Biol, 241:533-540, 2006. Models at modelarchive.org ma-chxa5 and ma-c88vd