Coggins L W, O'Prey M
Beatson Institute for Cancer Research, Bearsden, Glasgow, UK.
Nucleic Acids Res. 1989 Sep 25;17(18):7417-26. doi: 10.1093/nar/17.18.7417.
DNA tertiary structures are shown to be formed by denaturation and reannealing in vitro of molecularly-cloned DNA containing multiple tandem repeat sequences. Electron microscopy of homoduplex DNA molecules containing the human c-Harvey-ras gene revealed knot-like structures which mapped to the position of the 812 bp variable tandem repeat (VTR) sequence. We propose that the structures result from slipped-strand mispairing within the VTR and hybridisation of homologous repetitive sequences in the single-stranded loops so produced. Similar structures were also found in freshly-linearized supercoiled plasmids. More complex knot-like structures were found in homoduplexes of a 4 kb tandem array from the hypervariable region 3' to the human alpha-globin locus. Formation of such DNA tertiary structures in vitro also provides a practical method for identifying and mapping direct tandem repeat arrays that are at least 800 bp long.
DNA三级结构显示是由体外对含有多个串联重复序列的分子克隆DNA进行变性和复性而形成的。对含有人类c-Harvey-ras基因的同源双链DNA分子进行电子显微镜观察，发现了纽结状结构，这些结构定位于812 bp可变串联重复（VTR）序列的位置。我们认为这些结构是由VTR内的滑链错配以及由此产生的单链环中同源重复序列的杂交所致。在新鲜线性化的超螺旋质粒中也发现了类似的结构。在人α-珠蛋白基因座3'端高变区的一个4 kb串联阵列的同源双链中发现了更复杂的纽结状结构。体外形成这种DNA三级结构也为鉴定和定位至少800 bp长的直接串联重复阵列提供了一种实用方法。
