Studies on nucleic acid interactions I. Stabilities of mini-duplexes (dG2A4XA4G2.dC2T4YT4C2) and self-complementary d(GGGAAXYTTCCC) containing deoxyinosine and other mismatched bases

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Abstract
The thermal stability of DNA duplexes containing deoxyinosine in a pairing position in turn with each of the four major deoxynucleotides has been investigated by measuring ultraviolet-absorbance at different temperatures. d(G 2 A 4 × A 4 G 2 ) and d(C 2 T 4 YT 4 C 2 ) were prepared by the solid-phase phosphotriester method. When X is deoxyinosine, the Tm values of the duplexes are in the order Y=dC>dA>dG >dT>dU. The Tm of other duplexes containing dG, dA and dT at X were also measured. Self-complementary duplexes d(GGGAAINTTCCC) showed the same order of stability with N being dC, dA, dG and dT. Thermal stabilities of duplexes containing dG instead of dl were compared with other matched and mismatched duplexes. The Tm values of sequence isomers containing purine-pyrimidine combinations were compared. Self-complementary duplexes containing G-C and A-T in the central positions showed Tra values ca. 10° higher than those containing C-G and T-A in the same positions. Thermodynamic parameters and circular dichroism spectra of these oligonucleotides were compared.