Fischer Nicole, Weis Karsten
Department of Molecular and Cell Biology, Division of Cell and Developmental Biology, University of California-Berkeley, Berkeley, CA 94720-3200, USA.
EMBO J. 2002 Jun 3;21(11):2788-97. doi: 10.1093/emboj/21.11.2788.
An important control step in the regulation of cytoplasmic mRNA turnover is the removal of the m(7)G cap structure at the 5' end of the message. Here, we describe the functional characterization of Dhh1, a highly conserved member of the family of DEAD box-containing proteins, as a regulator of mRNA decapping in Saccharomyces cerevisiae. Dhh1 is a cytoplasmic protein and is shown to be in a complex with the mRNA degradation factor Pat1/Mtr1 and with the 5'-3' exoribonuclease Xrn1. Dhh1 specifically affects mRNA turnover in the deadenylation-dependent decay pathway, but does not act on the degradation of nonsense-containing mRNAs. Cells that lack dhh1 accumulate degradation intermediates that have lost their poly(A) tail but contain an intact 5' cap structure, suggesting that Dhh1 is required for efficient decapping in vivo. Furthermore, recombinant Dhh1 is able to stimulate the activity of the purified decapping enzyme Dcp1 in an in vitro decapping assay. We propose that the DEAD box protein Dhh1 regulates the access of the decapping enzyme to the m(7)G cap by modulating the structure at the 5' end of mRNAs.
细胞质mRNA周转调控中的一个重要控制步骤是去除信使RNA 5'端的m（7）G帽结构。在此，我们描述了Dhh1的功能特性，它是含DEAD盒蛋白家族中一个高度保守的成员，作为酿酒酵母中mRNA去帽的调节因子。Dhh1是一种细胞质蛋白，已证明它与mRNA降解因子Pat1/Mtr1以及5'-3'外切核糖核酸酶Xrn1形成复合物。Dhh1特异性影响依赖于去腺苷酸化的衰变途径中的mRNA周转，但不作用于含无义密码子的mRNA的降解。缺乏dhh1的细胞会积累已失去其多聚（A）尾但含有完整5'帽结构的降解中间体，这表明Dhh1是体内有效去帽所必需的。此外，重组Dhh1能够在体外去帽试验中刺激纯化的去帽酶Dcp1的活性。我们提出，DEAD盒蛋白Dhh1通过调节mRNA 5'端的结构来调控去帽酶接近m（7）G帽的过程。
