Thermodynamic studies of base pairing involving 2,6-diaminopurine

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Abstract
The thermal stabilities of oligodeoxyribonucleotide duplexes containing 2,6-diaminopurine (D) matched with each of the four normal DNA bases were determined by optical melting techniques. Comparison of optical melting curves yielded relative stabilities for the D-containing standard base pairs in an otherwise identical base-pair sequence. The D:T pair was found to be more stable than the A:T pair in dC 3 DG 3 dC 3 TG 3 , as stable as the A:T in dCT 3 DT 3 G:dCA 3 TA 3 G, and less stable than the A:T in dCA 3 DA 3 G:dCT 7 G. The order of stabilities for X:Y in the DNA duplex dCA 3 XA 3 G:dCT 3 YT 3 G is: (A:T)>(T:D)≃(D:T)≥(T:A)>(C:D)≃(D:A)≃(D:G)≥(D:C)≃(G:D)≃(D:D)≥(A:D). Implications of these results for design of DNA oligonucleotide probes are discussed.