Hang B, Chenna A, Sági J, Singer B
Donner Laboratory, Lawrence Berkeley National Laboratory, University of California, Berkeley 94720, USA.
Carcinogenesis. 1998 Aug;19(8):1339-43. doi: 10.1093/carcin/19.8.1339.
We report here that the newly synthesized DNA adduct, 1,N6-benzetheno-dA (pBQ-dA), in defined oligonucleotides [Chenna and Singer, Chem. Res. Toxicol., 8, 865-874], is a substrate for the major human AP endonuclease, HAP1, and the Escherichia coli AP endonucleases, exonuclease III and endonuclease IV. The mechanism of cleavage is identical to that reported previously for 3,N4-benzetheno-dC (pBQ-dC) and leads to a phosphodiester bond cleavage 5' to the adduct. There are, however, significant differences in the rate of cleavage of this adduct by these enzymes. The two bacterial AP endonucleases are both much more efficient than the human repair enzyme. In addition, using two random oligodeoxynucleotide sequences containing a single pBQ-dA, exonuclease III and endonuclease IV are similarly active, while HAP1 shows a distinct sequence preference of approximately 10-fold in efficiency of cleavage. The repair of this adduct by the three recombinant enzymes is further confirmed by using both active site mutant HAP1 proteins and by E.coli mutant strains lacking exonuclease III and/ or endonuclease IV. This sequence-dependent repair of pBQ-dA by HAP1 may play an important role in modulating benzene-induced carcinogenesis.
我们在此报告，新合成的DNA加合物1,N6-苯并乙烯基-dA（pBQ-dA）存在于特定的寡核苷酸中[Chenna和Singer，《化学研究毒理学》，8，865 - 874]，它是主要的人类AP核酸内切酶HAP1以及大肠杆菌AP核酸内切酶核酸外切酶III和核酸内切酶IV的底物。切割机制与先前报道的3,N4-苯并乙烯基-dC（pBQ-dC）相同，导致加合物5'端的磷酸二酯键断裂。然而，这些酶切割该加合物的速率存在显著差异。两种细菌AP核酸内切酶的效率均远高于人类修复酶。此外，使用两个含有单个pBQ-dA的随机寡脱氧核苷酸序列，核酸外切酶III和核酸内切酶IV的活性相似，而HAP1在切割效率上表现出约10倍的明显序列偏好。通过使用活性位点突变的HAP1蛋白以及缺乏核酸外切酶III和/或核酸内切酶IV的大肠杆菌突变菌株，进一步证实了这三种重组酶对该加合物的修复作用。HAP1对pBQ-dA的这种序列依赖性修复可能在调节苯诱导的致癌作用中起重要作用。
