Bush Maxwell S, Pierrat Olivier, Nibau Candida, Mikitova Veronika, Zheng Tao, Corke Fiona M K, Vlachonasios Konstantinos, Mayberry Laura K, Browning Karen S, Doonan John H
Department of Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom (M.S.B., O.P., V.M.);Institute of Biological, Environmental, and Rural Sciences, Aberystwyth University, Gogerddan Campus, Aberystwyth SY23 3EE, United Kingdom (C.N., F.M.K.C., K.V., J.H.D.);Institute of Virology and Biotechnology, Zhejiang Academy of Agricultural Science, Hangzhou City, Zhejiang Province 310021, China (T.Z.);Aristotle University of Thessaloniki, Faculty of Science, School of Biology, Department of Botany, 54124 Thessaloniki, Greece (K.V.); andDepartment of Molecular Biosciences and Institute for Cell and Molecular Biology, University of Texas, Austin, Texas 78712 (L.K.M., K.S.B.).
Department of Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom (M.S.B., O.P., V.M.);Institute of Biological, Environmental, and Rural Sciences, Aberystwyth University, Gogerddan Campus, Aberystwyth SY23 3EE, United Kingdom (C.N., F.M.K.C., K.V., J.H.D.);Institute of Virology and Biotechnology, Zhejiang Academy of Agricultural Science, Hangzhou City, Zhejiang Province 310021, China (T.Z.);Aristotle University of Thessaloniki, Faculty of Science, School of Biology, Department of Botany, 54124 Thessaloniki, Greece (K.V.); andDepartment of Molecular Biosciences and Institute for Cell and Molecular Biology, University of Texas, Austin, Texas 78712 (L.K.M., K.S.B.)
Plant Physiol. 2016 Sep;172(1):128-40. doi: 10.1104/pp.16.00435. Epub 2016 Jul 7.
Eukaryotic initiation factor 4A (eIF4A) is a highly conserved RNA-stimulated ATPase and helicase involved in the initiation of messenger RNA translation. Previously, we found that eIF4A interacts with cyclin-dependent kinase A (CDKA), the plant ortholog of mammalian CDK1. Here, we show that this interaction occurs only in proliferating cells where the two proteins coassociate with 5'-cap-binding protein complexes, eIF4F or the plant-specific eIFiso4F. CDKA phosphorylates eIF4A on a conserved threonine residue (threonine-164) within the RNA-binding motif 1b TPGR. In vivo, a phospho-null (APGR) variant of the Arabidopsis (Arabidopsis thaliana) eIF4A1 protein retains the ability to functionally complement a mutant (eif4a1) plant line lacking eIF4A1, whereas a phosphomimetic (EPGR) variant fails to complement. The phospho-null variant (APGR) rescues the slow growth rate of roots and rosettes, together with the ovule-abortion and late-flowering phenotypes. In vitro, wild-type recombinant eIF4A1 and its phospho-null variant both support translation in cell-free wheat germ extracts dependent upon eIF4A, but the phosphomimetic variant does not support translation and also was deficient in ATP hydrolysis and helicase activity. These observations suggest a mechanism whereby CDK phosphorylation has the potential to down-regulate eIF4A activity and thereby affect translation.
真核生物起始因子4A（eIF4A）是一种高度保守的RNA刺激型ATP酶和解旋酶，参与信使核糖核酸翻译的起始过程。此前，我们发现eIF4A与细胞周期蛋白依赖性激酶A（CDKA）相互作用，CDKA是哺乳动物CDK1在植物中的同源物。在此，我们表明这种相互作用仅发生在增殖细胞中，这两种蛋白在增殖细胞中与5'-帽结合蛋白复合物eIF4F或植物特异性的eIFiso4F共同结合。CDKA在RNA结合基序1b的TPGR内一个保守的苏氨酸残基（苏氨酸-164）上使eIF4A磷酸化。在体内，拟南芥eIF4A1蛋白的磷酸化缺失（APGR）变体保留了在功能上互补缺乏eIF4A1的突变体（eif4a1）植株系的能力，而磷酸化模拟（EPGR）变体则不能互补。磷酸化缺失变体（APGR）挽救了根和莲座叶的缓慢生长速率，以及胚珠败育和晚花表型。在体外，野生型重组eIF4A1及其磷酸化缺失变体均支持依赖eIF4A的无细胞小麦胚提取物中的翻译，但磷酸化模拟变体不支持翻译，并且在ATP水解和解旋酶活性方面也存在缺陷。这些观察结果提示了一种机制，即CDK磷酸化有可能下调eIF4A的活性，从而影响翻译。
