Ljungquist S
J Biol Chem. 1977 May 10;252(9):2808-14.
A new DNA endonuclease has been purified 3000-fold from Escherichia coli. The enzyme specifically catalyzes the formation of single strand breaks at apurinic and apyrimidinic sites in DNA, but has no activity on intact or single-stranded DNA. Further, the enzyme shows little or no activity on heavily ultraviolet-irradiated DNA, but cleaves x-irradiated DNA, presumably at apurinic and apyrimidinic sites introduced by the radiation treatment. The enzyme, which is tentatively named endonuclease IV, has no detectable associated exonuclease or DNA N-glycosidase activity and does not seem to be identical with any previously known E. coli endonuclease. Endonuclease IV has no Mg2+ requirement, and is fully active in the presence of EDTA. Enzyme activity is stimulated by 0.2 to 0.3 M NaCl and is unusually salt-resistant. Further, the enzyme is fairly heat-stable, and is not inhibited by tRNA. The sidimentation coefficient, S(o)20,w, is 3.4 S. It seems that endonuclease IV is active in DNA repair.
一种新的DNA内切核酸酶已从大肠杆菌中纯化出来，纯化倍数达3000倍。该酶特异性催化DNA中脱嘌呤和脱嘧啶位点处单链断裂的形成，但对完整的或单链DNA无活性。此外，该酶对重度紫外线照射的DNA几乎没有活性，但能切割经x射线照射的DNA，推测是在辐射处理引入的脱嘌呤和脱嘧啶位点处切割。这种酶暂命名为内切核酸酶IV，未检测到相关的外切核酸酶或DNA N-糖苷酶活性，似乎与任何先前已知的大肠杆菌内切核酸酶都不相同。内切核酸酶IV不需要Mg2+，在EDTA存在下仍具有完全活性。酶活性受0.2至0.3M NaCl刺激，且具有异常的耐盐性。此外，该酶相当耐热，不受tRNA抑制。沉降系数S(o)20,w为3.4S。内切核酸酶IV似乎在DNA修复中具有活性。
