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首页> 外文期刊>Molecular and Cellular Biology >Distinct replication-independent and -dependent phases of histone gene expression during the Physarum cell cycle.
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Distinct replication-independent and -dependent phases of histone gene expression during the Physarum cell cycle.

机译：Physarum细胞周期中组蛋白基因表达的不同复制非依赖性和非依赖性相。

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During the S phase of the cell cycle, histone gene expression and DNA replication are tightly coupled. In mitotically synchronous plasmodia of the myxomycete Physarum polycephalum, which has no G1 phase, histone mRNA synthesis begins in mid-G2 phase. Although histone gene transcription is activated in the absence of significant DNA synthesis, our data demonstrate that histone gene expression became tightly coupled to DNA replication once the S phase began. There was a transition from the replication-independent phase to the replication-dependent phase of histone gene expression. During the first phase, histone mRNA synthesis appears to be under direct cell cycle control; it was not coupled to DNA replication. This allowed a pool of histone mRNA to accumulate in late G2 phase, in anticipation of future demand. The second phase began at the end of mitosis, when the S phase began, and expression became homeostatically coupled to DNA replication. This homeostatic control required continuing protein synthesis, since cycloheximide uncoupled transcription from DNA synthesis. Nuclear run-on assays suggest that in P. polycephalum this coupling occurs at the level of transcription. While histone gene transcription appears to be directly switched on in mid-G2 phase and off at the end of the S phase by cell cycle regulators, only during the S phase was the level of transcription balanced with the rate of DNA synthesis.
机译：在细胞周期的S期，组蛋白基因表达和DNA复制紧密结合。在没有G1期的粘菌多头的有丝分裂同步浆膜中，组蛋白mRNA合成在G2中期开始。尽管组蛋白基因转录在没有大量DNA合成的情况下被激活，但我们的数据表明，一旦S期开始，组蛋白基因的表达就与DNA复制紧密相关。从组蛋白基因表达的不依赖复制的阶段过渡到依赖复制的阶段。在第一个阶段，组蛋白的mRNA合成似乎处于直接的细胞周期控制之下。它没有与DNA复制耦合。这使得组蛋白mRNA池在G2期后期积累，以预期未来的需求。第二阶段始于有丝分裂的末期，即S期开始时，表达与DNA复制趋于稳态。这种稳态控制需要持续的蛋白质合成，因为环己酰亚胺使DNA合成的转录解偶联。核运行分析表明，在多头体育中，这种偶联发生在转录水平。虽然组蛋白基因转录似乎在G2中期直接被打开，在S期结束时被细胞周期调节剂直接关闭，但只有在S期，转录水平才与DNA合成速率保持平衡。

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