Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
Structure. 2012 Jun 6;20(6):1007-18. doi: 10.1016/j.str.2012.03.011. Epub 2012 May 3.
Polyadenylation regulation and efficient nuclear export of mature mRNPs both require the polyadenosine-RNA-binding protein, Nab2, which contains seven CCCH Zn fingers. We describe here the solution structure of fingers 5-7, which are necessary and sufficient for high-affinity polyadenosine-RNA binding, and identify key residues involved. These Zn fingers form a single structural unit. Structural coherence is lost in the RNA-binding compromised Nab2-C437S mutant, which also suppresses the rat8-2 allele of RNA helicase Dbp5. Structure-guided Nab2 variants indicate that dbp5(rat8-2) suppression is more closely linked to hyperadenylation and suppression of mutant alleles of the nuclear RNA export adaptor, Yra1, than to affinity for polyadenosine-RNA. These results indicate that, in addition to modulating polyA tail length, Nab2 has an unanticipated function associated with generating export-competent mRNPs, and that changes within fingers 5-7 lead to suboptimal assembly of mRNP export complexes that are more easily disassembled by Dbp5 upon reaching the cytoplasm.
聚腺苷酸化调节和成熟 mRNP 的有效核输出都需要多聚腺苷酸-RNA 结合蛋白 Nab2，它包含七个 CCCH Zn 指。我们在这里描述了第 5-7 个指的溶液结构，它们是高亲和力多聚腺苷酸-RNA 结合所必需和充分的，并且确定了涉及的关键残基。这些 Zn 指形成一个单一的结构单元。在 RNA 结合受损的 Nab2-C437S 突变体中，结构一致性丧失，该突变体也抑制 RNA 解旋酶 Dbp5 的 rat8-2 等位基因。结构导向的 Nab2 变体表明，dbp5(rat8-2)抑制与 hyperadenylation 以及核 RNA 输出衔接子 Yra1 的突变等位基因的抑制更为密切相关，而与多聚腺苷酸-RNA 的亲和力关系不大。这些结果表明，除了调节 polyA 尾巴的长度外，Nab2 还具有与生成有出口能力的 mRNP 相关的意外功能，并且在第 5-7 个指内的变化导致 mRNP 出口复合物的组装不最佳，当到达细胞质时，Dbp5 更容易使其解体。
