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首页> 外文期刊>Molecular and Cellular Biology >Temporal Activation of the Sea Urchin Late H1 Gene Requires Stage-Specific Phosphorylation of the Embryonic Transcription Factor SSAP
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Temporal Activation of the Sea Urchin Late H1 Gene Requires Stage-Specific Phosphorylation of the Embryonic Transcription Factor SSAP

机译：海胆H1晚期基因的暂时激活需要胚胎转录因子SSAP的特定阶段磷酸化。

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摘要

Stage-specific activator protein (SSAP) is a 41-kDa polypeptide that binds to embryonic enhancer elements of the sea urchin late H1 gene. These enhancer elements mediate the transcriptional activation of the late H1 gene in a temporally specific manner at the mid-blastula stage of embryogenesis. Although SSAP can transactivate the late H1 gene only at late stages of the development, it resides in the sea urchin nucleus and maintains DNA binding activity throughout early embryogenesis. In addition, it has been shown that SSAP undergoes a conversion from a 41-kDa monomer to a ～80- to 100-kDa dimer when the late H1 gene is activated. We have demonstrated that SSAP is differentially phosphorylated during embryogenesis. Serine 87, a cyclic AMP-dependent protein kinase consensus site located in the N-terminal DNA binding domain, is constitutively phosphorylated. At the mid-blastula stage of embryogenesis, temporally correlated with SSAP dimer formation and late H1 gene activation, a threonine residue in the C-terminal transactivation domain is phosphorylated. This phosphorylation can be catalyzed by a break-ended double-stranded DNA-activated protein kinase activity from the sea urchin nucleus in vitro. Microinjection of synthetic SSAP mRNAs encoding either serine or threonine phosphorylation mutants results in the failure to transactivate reporter genes that contain the enhancer element, suggesting that both serine and threonine phosphorylation of SSAP are required for the activation of the late H1 gene. Furthermore, SSAP can undergo blastula-stage-specific homodimerization through its GQ-rich transactivation domain. The late-specific threonine phosphorylation in this domain is essential for the dimer assembly. These observations indicate that temporally regulated SSAP activation is promoted by threonine phosphorylation on its transactivation domain, which triggers the formation of a transcriptionally active SSAP homodimer.
机译：阶段特异性激活蛋白（SSAP）是一种41 kDa多肽，可与海胆H1晚期基因的胚胎增强子结合。这些增强子元件在胚胎发生的囊胚中期以时间特异性方式介导晚期H1基因的转录激活。尽管SSAP只能在发育的晚期阶段才激活H1晚期基因，但它位于海胆核中，并在整个早期胚胎发生过程中保持DNA结合活性。另外，已经证明当晚期H1基因被激活时，SSAP经历了从41kDa的单体到〜80kDa至100kDa的二聚体的转化。我们已经证明，SSAP在胚胎发生过程中被差异磷酸化。丝氨酸87（位于N端DNA结合域中的环状AMP依赖性蛋白激酶共有位点）被组成型磷酸化。在胚发生的胚泡中期，在时间上与SSAP二聚体形成和晚期H1基因激活相关，C末端反式激活域中的苏氨酸残基被磷酸化。这种磷酸化可以被海胆核的末端断裂的双链DNA激活的蛋白激酶活性催化。微量注射编码丝氨酸或苏氨酸磷酸化突变体的合成SSAP mRNAs导致无法激活包含增强子元件的报告基因，这表明SSAP的丝氨酸和苏氨酸磷酸化都需要激活晚期H1基因。此外，SSAP可以通过其富含GQ的反式激活域经历囊胚期特异性均二聚化。该结构域中的晚期特异性苏氨酸磷酸化对于二聚体组装至关重要。这些观察结果表明，在时间上受调节的SSAP活化通过其反式激活域上的苏氨酸磷酸化来促进，这触发了转录活性SSAP同二聚体的形成。

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