Unk I, Haracska L, Prakash S, Prakash L
Sealy Center for Molecular Science, University of Texas Medical Branch, Galveston, Texas 77555-1061, USA.
Mol Cell Biol. 2001 Mar;21(5):1656-61. doi: 10.1128/MCB.21.5.1656-1661.2001.
In Saccharomyces cerevisiae, the AP endonucleases encoded by the APN1 and APN2 genes provide alternate pathways for the removal of abasic sites. Oxidative DNA-damaging agents, such as H(2)O(2), produce DNA strand breaks which contain 3'-phosphate or 3'-phosphoglycolate termini. Such 3' termini are inhibitory to synthesis by DNA polymerases. Here, we show that purified yeast Apn2 protein contains 3'-phosphodiesterase and 3'-->5' exonuclease activities, and mutation of the active-site residue Glu59 to Ala in Apn2 inactivates both these activities. Consistent with these biochemical observations, genetic studies indicate the involvement of APN2 in the repair of H(2)O(2)-induced DNA damage in a pathway alternate to APN1, and the Ala59 mutation inactivates this function of Apn2. From these results, we conclude that the ability of Apn2 to remove 3'-end groups from DNA is paramount for the repair of strand breaks arising from the reaction of DNA with reactive oxygen species.
在酿酒酵母中，由APN1和APN2基因编码的AP核酸内切酶为无碱基位点的去除提供了替代途径。氧化性DNA损伤剂，如H₂O₂，会产生含有3'-磷酸或3'-磷酸乙醇酸末端的DNA链断裂。这种3'末端会抑制DNA聚合酶的合成。在此，我们表明纯化的酵母Apn2蛋白具有3'-磷酸二酯酶和3'→5'核酸外切酶活性，并且Apn2中活性位点残基Glu59突变为Ala会使这两种活性均失活。与这些生化观察结果一致，遗传学研究表明APN2参与了在一条与APN1不同的途径中对H₂O₂诱导的DNA损伤的修复，并且Ala59突变使Apn2的这一功能失活。从这些结果中，我们得出结论，Apn2从DNA上去除3'末端基团的能力对于修复由DNA与活性氧反应产生的链断裂至关重要。
