Structural biology of human REV1, REV3 and REV7 complex

DNA聚合酶ζ(PolDNA聚合酶ζ)是一种参与跨病变DNA合成的容易出错的DNA聚合酶。POLζ由两个亚基组成：催化的Rev3属于B家族的DNA聚合酶，非催化的Rev7。Rev7还与Rev1聚合酶相互作用，Rev1聚合酶是一种容易出错的Y家族DNA聚合酶，也参与TLS。这三种REV蛋白中的一种的细胞和所有三种蛋白都缺乏的细胞表现出相似的表型，这表明三种REV蛋白的功能协同。Rev7同时与Rev3和Rev1聚合酶相互作用，但Rev7或Rev3的结构以及Rev1-Rev7和Rev3-Rev7相互作用的结构和功能基础尚不清楚。在这里，我们展示了第一个人Rev7与人Rev3聚合酶片段(残基1847-1898)的复合体的晶体结构，并揭示了Rev7-Rev3相互作用的机制。该结构表明Rev7和Rev3之间的相互作用为Rev1结合创建了一个结构界面。此外，我们还表明Rev7介导的相互作用与DNA损伤耐受性有关。我们的结果强调了Rev7作为一种适配器蛋白的功能，以将POLζ招募到病变部位。Rev7也被称为MAD2B或MAD2L2，还参与多种细胞功能，如信号转导和细胞周期调节。我们的结果将为理解Rev7-相互作用提供一般的结构基础。

DNA polymerase ζ (Polζ) is an error-prone DNA polymerase involved in translesion DNA synthesis (TLS). Polζ consists of two subunits: the catalytic REV3, which belongs to B-family DNA polymerase, and the non-catalytic REV7. REV7 also interacts with REV1 polymerase, which is an error-prone Y-family DNA polymerase and also involved in TLS. Cells deficient in one of the three REV proteins and those deficient in all three proteins show similar phenotype, indicating the functional collaboration of the three REV proteins. REV7 interacts with both REV3 and REV1 polymerases, but the structure of REV7 or REV3, as well as the structural and functional basis of the REV1-REV7 and REV3-REV7 interactions remains unknown. Here we show the first crystal structure of human REV7 in complex with a fragment of human REV3 polymerase (residues 1847-1898) and reveal the mechanism underlying REV7-REV3 interaction. The structure indicates that the interaction between REV7 and REV3 creates a structural interface for REV1-binding. Furthermore, we show that the REV7-mediated interactions are responsible for DNA-damage tolerance. Our results highlight the function of REV7 as an adapter protein to recruit Polζ to a lesion site. REV7 is alternatively called MAD2B or MAD2L2 and also involved in various cellular functions such as signal transduction and cell-cycle regulation. Our results will provide a general structural basis for understanding the REV7-interaction.