Tanaka Y, Kyogoku Y
Institute for Protein Research, Osaka University, Japan.
Nucleic Acids Symp Ser. 1995(34):89-90.
From the stereochemical modeling of a triple helix, the third poly(dT) strand can bind in anti-parallel direction to the poly(dA) strand from the major groove of the poly(dA)-poly(dT) double helix. We designed a single strand 46mer DNA named AP46 which may form an anti-parallel triple helix containing only ATT base triplet by folding back in the strand. The UV melting profile of AP46 showed an increase of absorbance at 260 nm as temperature was raised, but no obvious double transition points were observed. We examined the type of a triple helix by using 3'-5' exonuclease activity of T4 DNA polymerase. The digestion experiment indicates that an anti-parallel triple helix is not so stable even if it exists. This enzymatic method is useful for probing the secondary structure of DNA strand.
通过对三链螺旋的立体化学建模可知，第三条聚（dT）链可以从聚（dA）-聚（dT）双螺旋的大沟处以反平行方向与聚（dA）链结合。我们设计了一条名为AP46的46聚体单链DNA，它可以通过自身回折形成一个仅包含ATT碱基三联体的反平行三链螺旋。AP46的紫外熔解曲线显示，随着温度升高，260nm处的吸光度增加，但未观察到明显的双转变点。我们利用T4 DNA聚合酶的3'-5'外切核酸酶活性来检测三链螺旋的类型。消化实验表明，即使存在反平行三链螺旋，其稳定性也不高。这种酶促方法对于探测DNA链的二级结构很有用。
