Association of branched nucleic acids.

Various branched nucleic acids (bNA's) of the general formula, 5'-(N)xrA[2'-(N)y], 3'-(N)y, have been prepared and their association with complementary linear oligonucleotides has been studied. The binding of complementary sequences to bNA's (for instance when N = dT, x = 0; y = 10 or x = y = 10 and the complement is dA10) yields transition temperatures (Tm's) equal to or greater than those of the corresponding linear complexes of similar base composition. Furthermore, a saturation of binding is observed when the number of mole-equivalents of complementary sequence equals the number of "arms" less one (n-1), i.e., for the "Y"-shaped molecule, 5'-T10-rA[(2'-T10), 3'-T10]; n = 3, saturation occurs at two equivalents of complementary sequence. The significance of these results is discussed in terms of possible triple helix formation.