Fox C A, Wickens M
Department of Biochemistry, College of Agriculture and Life Sciences, University of Wisconsin, Madison 53706.
Genes Dev. 1990 Dec;4(12B):2287-98. doi: 10.1101/gad.4.12b.2287.
Certain maternal mRNAs lose their poly(A) tails during early development and concomitantly become translationally inactive. In this report we analyze the mechanism of poly(A) removal during frog oocyte maturation by injecting short synthetic RNAs. We demonstrate that removal of poly(A) during oocyte maturation is a default reaction: In the absence of any specific sequence information, poly(A) is removed. However, poly(A) removal can be prevented by specific sequences in the 3'-untranslated regions of certain maternal mRNAs. These sequences are also required for poly(A) addition during oocyte maturation and include AAUAAA and a nearby U-rich element. Mutations in either AAUAAA or the U-rich element cause loss of poly(A) and not merely a failure to extend the poly(A) tail. We infer that poly(A) addition is required to escape poly(A) loss. The enzyme that removes the poly(A) during oocyte maturation appears to be a 3'----5' nuclease that prefers a 3'-terminal poly(A) segment. We discuss possible mechanisms by which poly(A) addition might circumvent default poly(A) removal and consider whether poly(A) removal is also a default reaction in somatic cells. Finally, we consider the possible implications of our results for the selectivity of poly(A) addition and removal, and for translational regulation during early development.
某些母体mRNA在早期发育过程中失去其多聚腺苷酸尾巴，并随之变得翻译无活性。在本报告中，我们通过注射短的合成RNA来分析蛙卵母细胞成熟过程中多聚腺苷酸去除的机制。我们证明，卵母细胞成熟过程中多聚腺苷酸的去除是一种默认反应：在没有任何特定序列信息的情况下，多聚腺苷酸会被去除。然而，某些母体mRNA的3'非翻译区中的特定序列可以阻止多聚腺苷酸的去除。这些序列在卵母细胞成熟过程中对于多聚腺苷酸的添加也是必需的，包括AAUAAA和附近富含U的元件。AAUAAA或富含U的元件中的突变会导致多聚腺苷酸的丢失，而不仅仅是多聚腺苷酸尾巴延伸失败。我们推断，多聚腺苷酸的添加是为了避免多聚腺苷酸的丢失。在卵母细胞成熟过程中去除多聚腺苷酸的酶似乎是一种3'→5'核酸酶，它更喜欢3'末端的多聚腺苷酸片段。我们讨论了多聚腺苷酸添加可能规避默认多聚腺苷酸去除的可能机制，并考虑多聚腺苷酸去除在体细胞中是否也是一种默认反应。最后，我们考虑了我们的结果对多聚腺苷酸添加和去除的选择性以及早期发育过程中翻译调控的可能影响。
