Ling J, Li X, Wu X, Liu W
Shanghai Institute of Biochemistry, Academia Sinica, China.
Biol Chem Hoppe Seyler. 1995 Nov;376(11):637-41. doi: 10.1515/bchm3.1995.376.11.637.
Ribosome-inactivating proteins (RIPs) were demonstrated to exhibit a unique enzymatic activity on cleaving supercoiled double-stranded DNA into the nicked or linear form. Although there is an interaction between supercoiled DNA and RIP, no sequence-specific recognition was involved. Instead, RIPs recognize supercoiled DNA by conformational specificity. Negatively supercoiled DNA is the preferential conformation in the action of RIPs. When double-stranded DNA occurs in the supercoiled form, even if with lower linking number, RIPs can still convert it into nicked or linear form. Terminal-labelling experiments indicated that radioactivity was incorporated into putative 5'-ends of nicked or linear DNA generated by RIPs. We conclude that RIPs act as a novel supercoil-dependent endonuclease when they cleavage supercoiled DNA. The impossibility that contaminating enzymes in the RIP preparations cleaved the supercoiled DNA is briefly discussed.
核糖体失活蛋白（RIPs）被证明对将超螺旋双链DNA切割成带切口或线性形式具有独特的酶活性。尽管超螺旋DNA与RIP之间存在相互作用，但不涉及序列特异性识别。相反，RIPs通过构象特异性识别超螺旋DNA。负超螺旋DNA是RIPs作用中的优先构象。当双链DNA以超螺旋形式存在时，即使连接数较低，RIPs仍可将其转化为带切口或线性形式。末端标记实验表明，放射性被掺入由RIPs产生的带切口或线性DNA的推定5'末端。我们得出结论，当RIPs切割超螺旋DNA时，它们作为一种新型的依赖超螺旋的内切核酸酶起作用。文中简要讨论了RIP制剂中污染酶切割超螺旋DNA的可能性。
