Evidence for a dual role for TC4 protein in regulating nuclear structure and cell cycle progression.
Evidence for a dual role for TC4 protein in regulating nuclear structure and cell cycle progression.
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TC4 蛋白在调节核结构和细胞周期进程中发挥双重作用的证据。
DOI：
10.1083/jcb.125.4.705
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发表时间：
1994-05
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TC 4是一种ras样G蛋白，参与了连接有丝分裂开始和DNA复制完成的反馈途径。在这份报告中，我们发现TC4在核组装和细胞周期进程中的不同作用。突变体和野生型形式的TC4被添加到爪蟾卵提取物能够组装核周围的染色质模板在体外。我们发现突变的TC 4蛋白GTP结合缺陷（GDP结合形式）抑制核生长，并阻止DNA复制。在这些条件下的核运输接近正常水平。在使用在S期和M期之间循环的爪蟾卵的无细胞提取物的单独的一组实验中，GDP结合形式的TC 4具有显著的效果，即使在完全不存在核的情况下也阻断进入有丝分裂。这种突变型TC4蛋白对细胞周期进程的影响是通过p34cdc2酪氨酸和苏氨酸残基的磷酸化介导的，负调节cdc2激酶活性。因此，我们提供了直接的生物化学证据TC4在维持核结构和调节进入有丝分裂的信号通路中的作用。
TC4, a ras-like G protein, has been implicated in the feedback pathway linking the onset of mitosis to the completion of DNA replication. In this report we find distinct roles for TC4 in both nuclear assembly and cell cycle progression. Mutant and wild-type forms of TC4 were added to Xenopus egg extracts capable of assembling nuclei around chromatin templates in vitro. We found that a mutant TC4 protein defective in GTP binding (GDP-bound form) suppressed nuclear growth and prevented DNA replication. Nuclear transport under these conditions approximated normal levels. In a separate set of experiments using a cell-free extract of Xenopus eggs that cycles between S and M phases, the GDP- bound form of TC4 had dramatic effects, blocking entry into mitosis even in the complete absence of nuclei. The effect of this mutant TC4 protein on cell cycle progression is mediated by phosphorylation of p34cdc2 on tyrosine and threonine residues, negatively regulating cdc2 kinase activity. Therefore, we provide direct biochemical evidence for a role of TC4 in both maintaining nuclear structure and in the signaling pathways that regulate entry into mitosis.