由以往的研究得知髮夾式核酸三螺旋比含同數核酸三鹼基之線型者要穩定（Tsay, et al., Biomol J. Str. Dyn. 1995, 12, 1235-1245，及所載之相關參考資料）。我們在本篇論文中合成了兩組寡核酸鏈，它們主要的結構是在5'及3'端各有一個含十二個鹼基的寡核酸鏈。這兩個寡核酸鏈是用非寡核酸鏈O(CH_2 CH_2O)_3P(O)_2 O(CH_2 CH_2O)_3P(O)_2(QQ)或是用寡核酸鏈-TTTT-來連結。我們以圓二色及紫外光研究發珼含QQ之三螺旋的穩定度略遜於含-TTTT-之三螺旋。但如-TTTT-若能和目標物成鹼基對時，則除了形成三螺旋外也能形成雙螺旋。本文也討論了5-methy1-2'-deoxycytidine及5-bromo-2'-deoxycytidine對三螺旋形成之影響。
A hairpin type triplex is stable than a non-hairpin type one with the same number of base triads (Tsay, et al., Biomol. J. Str. Dyn. 1995, 72, 1235 and references therein). In this work a piece of oligodeoxyribonucleotide, 5'-G-A-G-G-C-A-G-A-G-A-G-A-C-A-C-C-A-A-T-G-G-G-A-A-T-C-C-C (CI28D), that is a mimic of human IGF 2 gene m-RNA from -17 to 11 in sequence (Bell et al., Nature 1984, 370, 775) was synthesized as a target for triple strand nucleic acid formation . Two dodecadeoxyribonucleotide, 5'-C-T-C-C-T-T-C-T-C-T-C-T and T-C-T-C-T-C-T-G-C-C-T-C-3' with a non-oligonucleotides O(CH_2 CH_2 O)_3 P(O)_2 O(CH_2 CH_2 O)_3 P(O)_2 (QQ) or with -T-T-T-T- (TTTT) linker were synthesized as probes. Both sequences are able to form triplexes with the 5'-end from-17 to -6 of the Cl28D. The triplexes formed by probes with TTTT linker is slightly stable than those with QQ as a linker. However, duplex has also been detected in case the linker is capable to base pair to the Cl28D. Thus, the usage of QQ linker may avoid the unnecessary base pair bindings. The effects of the triplex formation by insertion of 5-methyl-2'-deoxycytidine and 5-bromo-2'-deoxycytidine are also revealed and discussed.
