【摘要】 超凝集DNA是质粒DNA的一种特殊拓扑结构形式,最初在大肠杆菌SD108(topA+gyrB225)细胞中被发现.现在大肠杆菌DM800(topA-gyrB225)细胞中也发现了这种结构,这说明超凝集DNA的形成与细胞内旋转酶活性降低有直接关系,而与拓扑异构酶Ⅰ的存在与否无关.体外实验的结果显示,具有很强的正超螺旋松弛活性的拓扑异构酶Ⅳ可以将超凝集DNA完全松弛,这也证明质粒DNA的超凝集结构与超螺旋结构在细胞内是可以互变的.使用原子力显微镜对分离到的pBR322DNA超凝集结构进行分析,并与普通超螺旋进行比较,结果表明,超凝集DNA分子的结构发生了巨大的变化,其分子长度比正常超螺旋分子缩短了约30%,宽度和高度则增加了60%,结构更接近于A型DNA.另外,原子力显微镜研究结果表明,氯喹的嵌入并非改变了超凝集DNA的超螺旋状态,而是使其打结并最终压缩成一团.更多还原

【Abstract】 The supercondensed DNA, a special kind of topological structure of plasmid DNA, was firstly found in E. coli SD108(topA+ gyrB225). Now, this structure is also found in E. coli DM800(topA- gyrB225). The result indicates that the formation of supercondensed DNA is related with decrease of the activity of gyrase in vivo. Topoisomerase Ⅳ was proved to relax the supercondensed DNA completely in vitro, which suggested that the supercondensed DNA and the supercoiled DNA could transform to each other in cells. The supercondensed DNA samples were analyzed by atomic force microscopy and compared to supercoiled DNA. The results showed that the length of supercondensed DNA decreased about 30% and the width and height of double-strand increased about 60%, which indicates that the structure of double-strand of supercondensed DNA is much more similar to A-DNA than B-DNA. The results also showed that chloroquine intercalation did not change the supercoiling level of supercondensed DNA, but made it knot and compact.更多还原