DNA与限制性内切酶相互作用的AFM研究

AFM Studies of Interaction of DNA and Restriction Endonuclease

应用轻敲模式原子力显微镜得到了田解反应后的线性ＰＷＲ１３质粒ＤＮＡ和人体γ－珠蛋白基因启动于两个ＤＮＡ片段的图象。我们的ＡＦＭ研究表明，在羽降解反应中，限制性内切酶除了与ＤＮＡ分子上的专一性作用位点有结合，还存在一种非专一性结合，而且这种结合是随机性的。在我们的ＡＦＭ测量中，在ＤＮＡ双链上限制性内切酶ＨｉｎｄＩｌｌ非专一性结合处直径与高度均大于链端专一性结合的ＤＮＡ一因复合物直径和高度，反映出两者结合状态的不同。

With the digestion of restriction endonuclease Hind III, the circular PWRr plasmid DNA became two fragments:linear PWR13 plasmid DNA (2. 6kb) and human γ-globin gene promotor(about 480hp). The high resolution AFM images of the two DNA fragments have been got. The height and width of the two DNA fragments from our AFM studies were different from the,expected diameter of DNA double-helix. Our AFM studies showed Hind Ⅲ binding on nonspecific sites as well as binding on specific sites and the nonspesific binding was random. The enzyme binding on the nonspecific site coundn't cause a characteristic bending angle of DNA double-strands. Data showed that the size of nonspecific bindng enzymes was larger than the size of specific binding enzymes. It indicated that DNA-enzyme complexes have different conformations in nonspecific and specific binding. It is suggested that the endonucleases bind on nonspecific sites and then slide along the double helix to find the target sequence' Our studies gave the visuale evidences for this theory.