Riddles P W, Lehman I R
J Biol Chem. 1985 Jan 10;260(1):170-3.
Formation of D-loops during the exchange of strands between a circular single-stranded DNA and a completely homologous linear duplex proceeds optimally when the duplex DNA is added to the complex of recA protein and single-stranded DNA formed in the presence of single-stranded DNA-binding protein and ATP. D-loops are undetectable when 200 microM adenosine 5'-O-(thiotriphosphate) is substituted for ATP. D-loops can be formed in the presence of adenosine 5'-O-(thiotriphosphate) if recA protein is the last component added to the reaction. However, these D-loops, which depend upon homologous sequences, are unstable upon deproteinization and are formed to a more limited extent than the structures formed with ATP. This finding indicates that D-loops formed under these conditions may be largely nonintertwined paranemic structures rather than plectonemic structures in which two of the strands are interwoven. When adenosine 5'-O-(thiotriphosphate) is added to an ongoing reaction containing ATP, formation of plectonemic structures and ATP hydrolysis is inhibited to an equivalent extent. We, therefore, conclude that ATP hydrolysis is required for the formation of plectonemic structures.
当双链DNA添加到在单链DNA结合蛋白和ATP存在下形成的recA蛋白与单链DNA的复合物中时，环状单链DNA与完全同源的线性双链之间的链交换过程中D环的形成最为理想。当用200微摩尔的腺苷5'-O-（硫代三磷酸）替代ATP时，无法检测到D环。如果recA蛋白是反应中最后添加的成分，则在腺苷5'-O-（硫代三磷酸）存在下可以形成D环。然而，这些依赖同源序列的D环在脱蛋白后不稳定，并且形成的程度比用ATP形成的结构更有限。这一发现表明，在这些条件下形成的D环可能主要是不相互缠绕的平行排列结构，而不是两条链相互交织的螺旋结构。当将腺苷5'-O-（硫代三磷酸）添加到正在进行的含有ATP的反应中时，螺旋结构的形成和ATP水解受到同等程度的抑制。因此，我们得出结论，ATP水解是形成螺旋结构所必需的。
