Van Lancker J L, Tomura T
Chem Biol Interact. 1980 Aug;31(2):179-88. doi: 10.1016/0009-2797(80)90004-6.
The sequential actions of two enzymes believed to be involved in DNA repair, namely a mammalian endonuclease and the bacterial DNA polymerase I on psoralen bound 32P-labeled DNA, was studied. When ultraviolet-irradiated DNA is exposed to the sequential action of the endonuclease, the formation of single-strand breaks prepares the DNA for the exonucleolytic excision of thymine dimers. The mammalian endonuclease purified from rat liver to electrophoretic homogeneity is inactive on normal DNA, DNA irradiated at 360 nm or DNA mixed with psoralen without irradiation. Incubation of psoralen-bound DNA labeled with 32P with the endonuclease releases the isotope in the acid soluble indicating that psoralen-bound DNA is susceptible to the endonucleolytic attack. Sedimentation of DNA on sucrose gradients indicates that there is no collapse of the DNA molecule after treatment with the endonuclease. Moreover, there is no release of the adduct in the acid soluble after treatment with DNA polymerase, indicating that the 5--3 min exonucleolytic activity of that enzyme is impaired by the remaining crosslinks. The crosslinks also inhibit the incorporation of [3H] dATP in presence of DNA polymerase I.
研究了两种据信参与DNA修复的酶的连续作用，即一种哺乳动物核酸内切酶和细菌DNA聚合酶I对补骨脂素结合的32P标记DNA的作用。当紫外线照射的DNA暴露于核酸内切酶的连续作用时，单链断裂的形成使DNA为胸腺嘧啶二聚体的核酸外切酶切除做好准备。从大鼠肝脏纯化至电泳纯的哺乳动物核酸内切酶对正常DNA、在360nm照射的DNA或未照射但与补骨脂素混合的DNA均无活性。用核酸内切酶孵育32P标记的补骨脂素结合DNA会使同位素释放到酸溶性部分，表明补骨脂素结合DNA易受核酸内切酶攻击。DNA在蔗糖梯度上的沉降表明，用核酸内切酶处理后DNA分子没有塌陷。此外，用DNA聚合酶处理后酸溶性部分没有加合物释放，表明该酶的5'-3'核酸外切酶活性受到剩余交联的损害。交联也会在DNA聚合酶I存在的情况下抑制[3H] dATP的掺入。
