Sánchez Ricardo, Marzluff William F
Program in Molecular Biology and Biotechnology, Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Mol Cell Biol. 2004 Mar;24(6):2513-25. doi: 10.1128/MCB.24.6.2513-2525.2004.
Metazoan replication-dependent histone mRNAs end in a stem-loop sequence. The one known exception is the histone mRNA in amphibian oocytes, which has a short oligo(A) tail attached to the stem-loop sequence. Amphibian oocytes also contain two proteins that bind the 3' end of histone mRNA: xSLBP1, the homologue of the mammalian SLBP, and xSLBP2, which is present only in oocytes. xSLBP2 is an inhibitor of histone mRNA translation, while xSLBP1 activates translation. The short A tail on histone mRNAs appears at stage II to III of oogenesis and is present on histone mRNAs throughout the rest of oogenesis. At oocyte maturation, the oligo(A) tail is removed and the xSLBP2 is degraded, resulting in the activation of translation of histone mRNA. Both SLBPs bind to the stem-loop with the oligo(A) tail with similar affinities. Reporter mRNAs ending in the stem-loop with or without the oligo(A) tail are translated equally well in a reticulocyte lysate, and their translation is stimulated by the presence of xSLBP1. In contrast, translation of the reporter mRNA with an oligo(A) tail is not activated in frog oocytes in response to the presence of xSLBP1. These results suggest that the oligo(A) tail is an active part of the translation repression mechanism that silences histone mRNA during oogenesis and that its removal is part of the mechanism that activates translation.
后生动物中，依赖复制的组蛋白mRNA以茎环序列结尾。已知的唯一例外是两栖动物卵母细胞中的组蛋白mRNA，其茎环序列上连接着一个短的寡聚腺苷酸尾巴。两栖动物卵母细胞还含有两种与组蛋白mRNA 3'末端结合的蛋白质：xSLBP1，即哺乳动物SLBP的同源物，以及仅存在于卵母细胞中的xSLBP2。xSLBP2是组蛋白mRNA翻译的抑制剂，而xSLBP1则激活翻译。组蛋白mRNA上的短A尾巴出现在卵子发生的II至III期，并在卵子发生的其余阶段一直存在于组蛋白mRNA上。在卵母细胞成熟时，寡聚腺苷酸尾巴被去除，xSLBP2被降解，从而导致组蛋白mRNA翻译的激活。两种SLBP以相似的亲和力与带有寡聚腺苷酸尾巴的茎环结合。以带有或不带有寡聚腺苷酸尾巴的茎环结尾的报告基因mRNA在网织红细胞裂解物中的翻译效果相同，并且它们的翻译受到xSLBP1的刺激。相比之下，在蛙卵母细胞中，带有寡聚腺苷酸尾巴的报告基因mRNA的翻译不会因xSLBP1的存在而被激活。这些结果表明，寡聚腺苷酸尾巴是卵子发生过程中使组蛋白mRNA沉默的翻译抑制机制的一个活跃部分，其去除是激活翻译机制的一部分。
