de Moor C H, Richter J D
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical Center, Worcester 01655, USA.
Mol Cell Biol. 1997 Nov;17(11):6419-26. doi: 10.1128/MCB.17.11.6419.
Cytoplasmic polyadenylation controls the translation of several maternal mRNAs during Xenopus oocyte maturation and requires two sequences in the 3' untranslated region (UTR), the U-rich cytoplasmic polyadenylation element (CPE), and the hexanucleotide AAUAAA. c-mos mRNA is polyadenylated and translated soon after the induction of maturation, and this protein kinase is necessary for a kinase cascade culminating in cdc2 kinase (MPF) activation. Other mRNAs are polyadenylated later, around the time of cdc2 kinase activation. To determine whether there is a hierarchy in the cytoplasmic polyadenylation of maternal mRNAs, we ablated c-mos mRNA with an antisense oligonucleotide. This prevented histone B4 and cyclin A1 and B1 mRNA polyadenylation, indicating that the polyadenylation of these mRNAs is Mos dependent. To investigate a possible role of cdc2 kinase in this process, cyclin B was injected into oocytes lacking c-mos mRNA. cdc2 kinase was activated, but mitogen-activated protein kinase was not. However, polyadenylation of cyclin B1 and histone B4 mRNA was still observed. This demonstrates that cdc2 kinase can induce cytoplasmic polyadenylation in the absence of Mos. Our data further indicate that although phosphorylation of the CPE binding protein may be involved in the induction of Mos-dependent polyadenylation, it is not required for Mos-independent polyadenylation. We characterized the elements conferring Mos dependence (Mos response elements) in the histone B4 and cyclin B1 mRNAs by mutational analysis. For histone B4 mRNA, the Mos response elements were in the coding region or 5' UTR. For cyclin B1 mRNA, the main Mos response element was a CPE that overlaps with the AAUAAA hexanucleotide. This indicates that the position of the CPE can have a profound influence on the timing of cytoplasmic polyadenylation.
细胞质聚腺苷酸化在非洲爪蟾卵母细胞成熟过程中控制着几种母源mRNA的翻译，并且需要3'非翻译区（UTR）中的两个序列，即富含尿苷的细胞质聚腺苷酸化元件（CPE）和六核苷酸AAUAAA。c-mos mRNA在成熟诱导后不久就会进行聚腺苷酸化并被翻译，并且这种蛋白激酶对于最终导致cdc2激酶（MPF）激活的激酶级联反应是必需的。其他mRNA在稍后，即cdc2激酶激活时进行聚腺苷酸化。为了确定母源mRNA的细胞质聚腺苷酸化是否存在层级关系，我们用反义寡核苷酸消除了c-mos mRNA。这阻止了组蛋白B4以及细胞周期蛋白A1和B1 mRNA的聚腺苷酸化，表明这些mRNA的聚腺苷酸化依赖于Mos。为了研究cdc2激酶在此过程中的可能作用，将细胞周期蛋白B注射到缺乏c-mos mRNA的卵母细胞中。cdc2激酶被激活，但丝裂原活化蛋白激酶未被激活。然而，仍然观察到细胞周期蛋白B1和组蛋白B4 mRNA的聚腺苷酸化。这表明在没有Mos的情况下，cdc2激酶可以诱导细胞质聚腺苷酸化。我们的数据进一步表明，虽然CPE结合蛋白的磷酸化可能参与了Mos依赖性聚腺苷酸化的诱导，但对于非Mos依赖性聚腺苷酸化来说并非必需。我们通过突变分析对组蛋白B4和细胞周期蛋白B1 mRNA中赋予Mos依赖性的元件（Mos反应元件）进行了表征。对于组蛋白B4 mRNA，Mos反应元件位于编码区或5'UTR中。对于细胞周期蛋白B1 mRNA，主要的Mos反应元件是一个与AAUAAA六核苷酸重叠的CPE。这表明CPE的位置对细胞质聚腺苷酸化的时间有深远影响。
