Double and triple helix formation of 2'-5' and 3'-5' oligonucleotides.

Double and triple helix formation of non-self complementary 2'-5' and 3'-5' linked oligonucleotides, 3'-5'(pA)7, 3'-5'(pU)7, 2'-5'(pA)7 and 2'-5'(pU)7, was studied using UV and CD spectroscopies. UV mixing curve and UV melting curve showed that 3'-5'(pA)7:3'-5' (pU)7 system could form double and triple helix, while 2'-5'(pA)7:2'-5'(pU)7 system could form only double helix and 3'-5'(pA)7:2'-5'(pU)7 system could form neither double nor triple helix under the condition examined. Thermodynamic parameters obtained from the UV melting curve indicate that the linkage type of oligonucleotides has profound effect on the helix formation.