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首页> 外文期刊>Molecular and Cellular Biology >Overexpression of an activated rasG gene during growth blocks the initiation of Dictyostelium development.
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Overexpression of an activated rasG gene during growth blocks the initiation of Dictyostelium development.

机译：生长期间激活的rasG基因的过表达会阻止Dictyostelium发育的启动。

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Transformants that expressed either the wild-type rasG gene, an activated rasG-G12T gene, or a dominant negative rasG-S17N gene, all under the control of the folate-repressible discoidin (dis1gamma) promoter, were isolated. All three transformants expressed high levels of Ras protein which were reduced by growth in the presence of folate. All three transformants grew slowly, and the reduction in growth rate correlated with the amount of RasG protein produced, suggesting that RasG is important in regulating cell growth. The pVEII-rasG transformant containing the wild-type rasG gene developed normally despite the presence of high levels of RasG throughout development. This result indicates that the down regulation of rasG that normally occurs during aggregation of wild-type strains is not essential for the differentiation process. Dictyostelium transformants expressing the dominant negative rasG-S17N gene also differentiated normally. Dictyostelium transformants that overexpressed the activated rasG-G12T gene did not aggregate. The defect occurred very early in development, since the expression of car1 and pde, genes that are normally induced soon after the initiation of development, was repressed. However, when the transformant cells were pulsed with cyclic AMP, expression of both genes returned to wild-type levels. The transformants exhibited chemotaxis to cyclic AMP, and development was synergized by mixing with wild-type cells. Furthermore, cells that were pulsed with cyclic AMP for 4 h before being induced to differentiate by plating on filters produced small, but otherwise normal, fruiting bodies. These results suggest that the rasG-G12T transformants are defective in cyclic AMP production and that RasG - GTP blocks development by interfering with the initial generation of cyclic AMP pulses.
机译：分离出表达了野生型rasG基因，激活的rasG-G12T基因或显性负性rasG-S17N基因的转化子，这些转化子均受叶酸可抑制的discoidin（dis1gamma）启动子控制。所有三个转化体均表达高水平的Ras蛋白，但在叶酸存在下生长会降低这些蛋白。所有三个转化体生长缓慢，并且生长速率的降低与产生的RasG蛋白量相关，这表明RasG在调节细胞生长中很重要。尽管整个发育过程中存在高水平的RasG，但包含野生型rasG基因的pVEII-rasG转化子仍能正常发育。该结果表明通常在野生型菌株聚集期间发生的rasG的下调对于分化过程不是必需的。表达显性负性rasG-S17N基因的双歧杆菌转化体也正常分化。过表达激活的rasG-G12T基因的盘基网柄菌转化子没有聚集。该缺陷发生在发育的很早，因为抑制了通常在发育开始后立即诱导的基因car1和pde的表达。但是，当用环状AMP对转化细胞进行脉冲处理时，两个基因的表达均恢复到野生型水平。转化子表现出对环AMP的趋化性，并且通过与野生型细胞混合而协同发育。此外，在通过平板接种于滤膜诱导分化之前，用环状AMP脉冲4 h的细胞会产生小的但正常的子实体。这些结果表明，rasG-G12T转化子在循环AMP产生中存在缺陷，并且RasG-GTP通过干扰循环AMP脉冲的初始生成来阻止发育。

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