Human exonuclease I is required for 5′ and 3′ mismatch repair.
Human exonuclease I is required for 5′ and 3′ mismatch repair.
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DOI：
10.1074/jbc.m111854200
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发表时间：
2002-04-12
影响因子：
4.8
通讯作者：
Modrich, P
中科院分区：
文献类型：
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作者：
Genschel, J;Bazemore, LR;Modrich, P
我们部分纯化了一种人类活性，它能使缺乏一种或多种错配修复切除活性的人类核提取物组分恢复错配依赖的双向切除能力。人类EXO1与切除活性共同纯化，并且纯化后的活性可由近乎均一的重组hEXO1替代。尽管该活性据报道具有5'到3'的水解极性，但hEXO1参与由位于错配碱基对5'或3'的链断裂所引导的错配激发的切除。当引导修复的链断裂位于错配碱基对的3'端时，在缺乏切除活性的提取物中，hEXO1和错配依赖的缺口形成需要hMutSα和hMutLα。然而，由5'链断裂引导的切除需要hMutSα，但在没有hMutLα的情况下也可发生。在由纯组分组成的系统中，hEXO1的5'到3'水解活性由hMutSα以错配依赖的方式激活。这些观察结果表明hEXO1在5' - 异源双链修复中具有水解功能。hEXO1参与3' - 异源双链修复表明它在3' - 切除复合物的组装中具有调节/结构作用，或者该蛋白具有一种隐蔽的3'到5'水解活性。
We have partially purified a human activity that restores mismatch-dependent, bi-directional excision to a human nuclear extract fraction depleted for one or more mismatch repair excision activities. Human EXOI copurifies with the excision activity, and the purified activity can be replaced by near homogeneous recombinant hEXOI. Despite the reported 5' to 3' hydrolytic polarity of this activity, hEXOI participates in mismatch-provoked excision directed by a strand break located either 5' or 3' to the mispair. When the strand break that directs repair is located 3' to the mispair, hEXOI- and mismatch-dependent gap formation in excision-depleted extracts requires both hMutSalpha and hMutLalpha. However, excision directed by a 5' strand break requires hMutSa but can occur in absence of hMutLa. In systems comprised of pure components, the 5' to 3' hydrolytic activity of hEXOI is activated by hMutSa in a mismatch-dependent manner. These observations indicate a hydrolytic function for hEXOI in 5'-heteroduplex correction. The involvement of hEXOI in 3'-heteroduplex repair suggests that it has a regulatory/structural role in assembly of the 3'-excision complex or that the protein possesses a cryptic 3' to 5' hydrolytic activity.