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首页> 外文期刊>Molecular and Cellular Biology >Phosphorylation of the RNA polymerase II largest subunit during Xenopus laevis oocyte maturation.
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Phosphorylation of the RNA polymerase II largest subunit during Xenopus laevis oocyte maturation.

机译：非洲爪蟾卵母细胞成熟过程中RNA聚合酶II最大亚基的磷酸化。

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Xenopus laevis oogenesis is characterized by an active transcription which ceases abruptly upon maturation. To survey changes in the characteristics of the transcriptional machinery which might contribute to this transcriptional arrest, the phosphorylation status of the RNA polymerase II largest subunit (RPB1 subunit) was analyzed during oocyte maturation. We found that the RPB1 subunit accumulates in large quantities from previtellogenic early diplotene oocytes up to fully grown oocytes. The C-terminal domain (CTD) of the RPB1 subunit was essentially hypophosphorylated in growing oocytes from Dumont stage IV to stage VI. Upon maturation, the proportion of hyperphosphorylated RPB1 subunits increased dramatically and abruptly. The hyperphosphorylated RPB1 subunits were dephosphorylated within 1 h after fertilization or heat shock of the matured oocytes. Extracts from metaphase II-arrested oocytes showed a much stronger CTD kinase activity than extracts from prophase stage VI oocytes. Most of this kinase activity was attributed to the activated Xp42 mitogen-activated protein (MAP) kinase, a MAP kinase of the ERK type. Making use of artificial maturation of the stage VI oocyte through microinjection of a recombinant stable cyclin B1, we observed a parallel activation of Xp42 MAP kinase and phosphorylation of RPB1. Both events required protein synthesis, which demonstrated that activation of p34(cdc2)off kinase was insufficient to phosphorylate RPB1 ex vivo and was consistent with a contribution of the Xp42 MAP kinase to RPB1 subunit phosphorylation. These results further support the possibility that the largest RNA polymerase II subunit is a substrate of the ERK-type MAP kinases during oocyte maturation, as previously proposed during stress or growth factor stimulation of mammalian cells.
机译：非洲爪蟾卵子发生的特征在于活跃的转录，该转录在成熟时突然终止。为了调查可能导致这种转录停滞的转录机制特征的变化，在卵母细胞成熟过程中分析了RNA聚合酶II最大亚基（RPB1亚基）的磷酸化状态。我们发现，RPB1亚基从前玻璃体形成的早期二倍体卵母细胞到完全生长的卵母细胞大量积累。在从Dumont阶段IV到阶段VI的生长卵母细胞中，RPB1亚基的C末端结构域（CTD）基本被磷酸化。成熟后，超磷酸化的RPB1亚基的比例急剧增加。在成熟卵母细胞受精或热激后1小时内，磷酸化的RPB1亚基被过度磷酸化。来自II期停滞卵母细胞的提取物显示出比前VI期卵母细胞的提取物更强的CTD激酶活性。该激酶活性的大部分归因于活化的Xp42丝裂原活化蛋白（MAP）激酶，这是ERK类型的MAP激酶。通过重组稳定的细胞周期蛋白B1的显微注射，利用VI期卵母细胞的人工成熟，我们观察到Xp42 MAP激酶和RPB1磷酸化的平行激活。这两个事件都需要蛋白质合成，这表明p34（cdc2）off激酶的激活不足以离体磷酸化RPB1，并且与Xp42 MAP激酶对RPB1亚基磷酸化的贡献一致。这些结果进一步支持了如下可能性：最大的RNA聚合酶II亚基是卵母细胞成熟期间ERK型MAP激酶的底物，如先前在哺乳动物细胞的应激或生长因子刺激期间提出的那样。

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