Ohshima K, Kang S, Larson J E, Wells R D
Department of Biochemistry and Biophysics, Texas A&M University, Texas Medical Center, Houston, Texas 77030-3303, USA.
J Biol Chem. 1996 Jul 12;271(28):16784-91. doi: 10.1074/jbc.271.28.16784.
CTG.CAG, CGG.CCG, and AAG.CTT triplet repeats proximal to or in disease genes expand by a non-Mendelian genetic process to cause several human hereditary syndromes. As part of our physical, biological, and genetic studies on the 10 possible triplet repeats, we discovered that the TTA.TAA repeat, isolated from the upstream region of the variant surface glycoprotein gene of Trypanosoma brucei, shows a propensity to adopt a non-H bonded structure under appropriate conditions. The other nine triplet repeat sequences do not exhibit this property. (TTA.TAA)n, where n = 90, 60, 30, and 18, cloned into pUC19 was studied by chemical and enzymatic probes as well as two-dimensional gel electrophoretic analyses under a variety of conditions. The helix opening was observed for all four inserts in supercoiled plasmids as a function of temperature, pH, metal ions, and buffer conditions using OsO4, diethyl pyrocarbonate, and chloroacetaldehyde probes. This unusual property of the TTA.TAA repeat suggests that it plays a different role from the other nine triplet repeats in gene expression.
疾病基因附近或内部的CTG.CAG、CGG.CCG和AAG.CTT三联体重复序列通过非孟德尔遗传过程发生扩增，从而导致多种人类遗传性综合征。作为我们对10种可能的三联体重复序列进行的物理、生物学和遗传学研究的一部分，我们发现，从布氏锥虫可变表面糖蛋白基因上游区域分离出的TTA.TAA重复序列在适当条件下倾向于形成非氢键结构。其他9种三联体重复序列则不具备这一特性。通过化学和酶促探针以及在各种条件下的二维凝胶电泳分析，对克隆到pUC19中的(TTA.TAA)n（其中n = 90、60、30和18）进行了研究。使用OsO4、焦碳酸二乙酯和氯乙醛探针，在超螺旋质粒中观察到所有四个插入片段的螺旋解旋随温度、pH值、金属离子和缓冲条件的变化。TTA.TAA重复序列的这种不寻常特性表明，它在基因表达中发挥着与其他9种三联体重复序列不同的作用。
