Polyxanthylic acid

In the homopolymers formed by uridine or 2-thiouridine, base pairs with twofold symmetry are feasible, as described in Part II, Chapter 16 [529, 699]. The situation is more complex, however, because the homopolymer folds back on itself, giving rise to a hairpin-like structure where the polynucleotide strands are necessarily antiparallel and the base pairs are of the form shown in Fig. 20.10. Not surprisingly, a comparable double helix is also observed for polyxanthylic acid poly (X) [700]. The purine base of xanthosine displays the same hydrogen-bonding functional groups as uracil and therefore, the same base pair can be formed, but the purine-purine pair requires a larger separation between the glycosidic links and consequently a wider helix radius. 

Arnott S, Chandrasekharan R, Day AW, Puigjaner LC, Watts L (1981) Double helical structures for polyxanthylic acid. J Mol Biol 149 489-505... 

Some other polynucleotide complexes. Polyxanthylic acid [poly(X)l forms complexes of various stoichiometries (1 1, 1 2, 2 1) with poly(U) and/or poly(l) (30). 

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See also in sourсe #XX -- [ ]

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